Catenated phosphorus materials and their preparation

ABSTRACT

High phosphorus polyphosphides, namely MP x , where M is an alkali metal (Li, Na, K, Rb, and Cs) or metals mimicking the bonding behavior of an alkali metal, and x=7 to 15 or very much greater than 15 (new forms of phosphorus) are useful semiconducutors in their crystalline, polycrystalline and amorphous forms (boules and films). MP 15  appears to have the best properties and KP 15  is the easier to synthesize. P may include other pnictides as well as other trivalent atomic species. Resistance lowering may be accomplished by doping with Ni, Fe, Cr, and other metals having occupied d or f outer electronic levels; or by incorporation of As and other pnictides. Top contacts forming junction devices doped with Ni and employing Ni as a back contact comprise Cu, Al, Mg, Ni, Au, Ag, and Ti. Photovoltaic, photoresistive, and photoluminescent devices are also disclosed. All semiconductor applications appear feasible. 
     These semiconductors belong to the class of polymer forming, trivalent atomic species forming homatomic, covalent bonds having a coordination number slightly less than 3. The predominant local order appears to be all parallel pentagonal tubes in all forms, including amorphous, except for the monoclinic and twisted fiber allotropes of phosphorus. 
     Large crystal monoclinic phosphorus (a birefringent material) in two habits, a twisted fiber phosphorus allotrope and a star shaped fibrous high phosphorus material are also disclosed. 
     Single and multiple source vapor transport, condensed phase, melt quench, flash evaporation, chemical vapor deposition, and molecular flow deposition may be employed in synthesizing these materials. Vapor transport may be employed to purify phosphorus. 
     The materials may be employed as protective coatings, optical coatings, fire retardants, fillers and reinforcing fillers for plastics and glasses, antireflection coatings for infrared optics, infrated transmitting windows, and optical rotators.

RELATED APPLICATIONS

This application is a divisional application of our co-pending U.S.Patent Applicaiton entitled CATENATED PHOSPHOROUS MATERIALS, THEIRPREPARATION AND USES, AND SEMICONDUCTOR AND OTHER DEVICES EMPLOYINGTHEM, Ser. No. 442,208, filed Nov. 16, 1984 now U.S. Pat. No. 4,508.931,which was a continuation-in-part of our copending applications entitledCATENATED SEMICONDUCTOR MATERIALS OF PHOSPHORUS, METHODS AND APPARATUSFOR PREPARING AND DEVICE USING THEM, Ser. No. 335,706, filed Dec. 30,1981, now abandoned; and MONOCLINIC PHOSPHORUS FORMED FROM VAPOR IN THEPRESENCE OF AN ALKALI METAL, Ser. No. 419,537, filed Sept 17, 1982 nowU.S. Pat. No. 4,620,968.

This application is also related to the following co-pendingapplications, assigned to the same assignee as this application. Theseapplications are incorporated herein by reference. VACUUM EVAPORATEDFILMS OF CATENATED PHOSPHORUS MATERIAL, Ser. No. 509,159, filed June 29,1983; GRAPHITE INTERCALATED ALKALI METAL VAPOR SOURCES, Ser. No.509,157, filed June 29, 1983; SPUTTERED SEMICONDUCTING FILMS OFCATENATED PHOSPHORUS MATERIAL AND DEVICES FORMED THEREFROM, Ser. No.509,175, filed June 29, 1983; MIS DEVICES EMPLOYING ELEMENTAL PNICTIDEOR POLYPHOSPHIDE INSULATING LAYERS, Ser. No. 509,210, June 29, 1983;LIQUID PHASE GROWTH OF CRYSTALLINE POLYPHOSPHIDE, Ser. No. 509,158,filed June 29, 1983; THERMAL CRACKERS FOR FORMING PNICTIDE FILMS IN HIGHVACUUM PROCESSES, Ser. No. 581,139, filed Feb. 17, 1984; PASSIVATION ANDINSULATION OF III-V DEVICES WITH PNICTIDES, PARTICULARLY AMORPHOUSPNICTIDES HAVING A LAYER-LIKE STRUCTURE, Ser. No. 581,115, filed Feb.17, 1984; PNICTIDE BARRIERS IN QUANTUM WELL DEVICES Ser. No. 581,140,filed Feb. 17, 1984; USE OF PNICTIRDE FILMS FOR WAVE-GUIDING INOPTO-ELECTRONIC DEVICES, Ser. No. 581,171, filed Feb. 17, 1984; VACUUMDEPOSITION PROCESSES EMPLOYING A CONTINUOUS PNICTIDE DELIVERY SYSTEM,PARTICULARLY SPUTTERING, Ser. No. 581,103, filed Feb. 17, 1984;CONTINUOUS PNICTIDE SOURCE AND DELIVERY SYSTEM FOR FILM DEPOSITION,PARTICULARLY BY CHEMICAL VAPOR DEPOSITION, Ser. No. 581,102, filed Feb.17, 1984; METHOD OF PREPARING HIGH PURITY WHITE PHOSPHORUS, Ser. No.581,105, filed Feb. 17, 1984; PNICTIDE TRAP FOR VACUUM SYSTEMS, Ser. No.581,101, filed Feb. 17, 1984; HIGH VACUUM DEPOSITION PROCESSES EMPLOYINGA CONTINUOUS PNICTIDE DELIVERY SYSTEM, Ser. No. 581,104, filed Feb. 17,1984; and THIN FILM FIELD EFFECT TRANSISTORS UTILIZING A POLYPNICTIDESEMICONDUCTOR, Ser. No. 619,053, filed June 11, 1984.

TECHNICAL FIELD

This invention relates to catenated phosphorus materials, theirpreparation and use, and to semiconductor and other devices employingthem. These materials include high phosphorus polyphosphides(i.e.,phosphides where the polymeric nature is maintained), alkali metalpolyphosphides, monoclinic phosphorus and new forms of phosphorus. Vaportransport is employed in making the crystalline, polycrystalline andamorphous phosphorus and polyphosphide materials in bulk, thick and thinfilms. Flash evaporation and chemical vapor deposition are used to makethin films. A condensed phase technique is utilized in producingcrystalline and polycrystalline polyphosphides. Diffusion doping isemployed to raise the conductivity of these materials. Rectifyingjunctions are formed on the materials by appropriate metal contacts. Thefilm materials may be used as optical coatings. Powdered crystals andamorphous materials may be used as fire retardant fillers. Thecrystalline materials, especially the fiberous forms, may be employed asthe high tensile components of reinforced plastics.

BACKGROUND ART

During the past several decades, the use of semiconductors has becomeever increasingly widespread and important. Silicon basedsemiconductors, for example, have generally been successful in providinga variety of useful devices, such as p-n junction rectifiers (diodes),transistors, silicon control rectifiers (SCR's), photovoltaic cells,light sensitive diodes, and the like. However, due to the high cost ofproducing crystalline silicon and the ever increasing demand forsemiconductors over a broadening range of applications, there has been aneed to widen correspondingly the scope of available usefulsemiconductor materials.

Useful semiconductors of the present invention, have an energy band gapin the range of about 1 to 3 eV (more specifically 1.4 to 2.2 eV); aphotoconductive ratio greater than 5, (more specifically between 100 and10,000); a conductivity between about 10⁻⁵ and 10⁻¹² (ohm-cm)⁻¹ (morespecifically conductivity in the range of 10⁸ to 10⁻⁹ (ohm-cm)); andchemical and physical stability under ambient operating conditions.Accordingly, while many materials may be semiconducting in the sensethey are not pure metals or pure insulators, only those semiconductingmaterials which meet these criteria may be considered to be usefulsemiconductors in the context of this invention.

Given the present need to develop alternative non-petroleum based energysources, the potential commercial utility of a semiconductor increasesdramatically when the semiconductor also exhibits an effectivephotovoltaic characteristic, that is, the ability to economically andefficiently convert solar energy into electrical potential.

From an economic standpoint, amorphous semiconductors, particularly inthe form of thin films, are more desirable than single crystalline formsdue to potential lower cost of production. Amorphous semiconductors alsohave better electrical qualities than polycrystalline forms of the samematerial are used in many semiconductor devices.

The semiconductor industry has continued its search for useful newsemiconductor materials beyond crystalline silicon, and the like.

In the non-silicon crystalline area, single crystals of semiconductingcompounds, including GaAs, GaP, and InP, are in commercial use.

Many other semiconductor materials have been utilized for specializedpurposes. For example, CdS and selenium are utilized as thephotoconductor in many xerographic machines.

In this application semiconductor device means a device including asemiconductor material whether the device employs electrical contacts,that is, is an electronic device, or whether it is a non-electronicdevice, such as the photoconductors employed in xerography,phosphorescent materials, the phosphorus in a cathode ray tube, or thelike.

Although some of the known forms of phosphorus have been stated to havesemiconducting properties, many are unstable, highly oxidizable andreactive, and no known form of phosphorus has been successfully employedas a useful semiconductor.

The group 3-5 materials such as gallium phosphide and indium phosphideare tetrahedrally bonded and thus, as will be pointed out below, areclearly distinguished from the compounds disclosed herein. Furthermore,their semiconducting properties are not dominated byphosphorus-to-phosphorus bonding, i.e. the primary conduction paths arenot the phosphorus-to-phosphorus bonds.

Others have disclosed hydrogenated phosphorus having a structure similarto black phosphorus and having semiconducting properties.

Considerable work on high phosphorus polyphosphides has been done by agroup headed by H. G. von Schnering. The various reports from this groupindicate that the highest phosphorus containing polyphosphide compoundthey have produced is crystalline MP₁₅ (M=group 1a metal). Thesepolyphosphides are produced by heating a mixture of metal and phosphorusin a sealed ampule. Von Schnering report that based on their structurepolyphosphides are classified as valence compounds in a classical sense,and that this means that these compounds are, or should be, insulatorsor semiconductors, i.e. not metals.

Monoclinic phosphorus, also called Hittorf's phosphorus, is preparedaccording to the prior art from white phosphorus and lead as follows: 1g of white phosphorus and 30 g of lead are heated slowly to a melt in asealed tube to 630° C. and held for a short time at that temperature.The solution is then cooled at the rate of 10° per day for 11 days to520° C., and cooled rapidly to room temperature thereafter. It is nextelectrolyzed in a solution of 2 kg of lead acetate in 8 liters of 6%acetic acid, and the phosphorus is collected in a watch glass placedunder the anode. Nearly square tabular crystals, about 0.2×0.2×0.05 mm,are obtained in this way.

The structure of this prior art monoclinic phosphorus has beendetermined by Thurn and Krebs. The crystals conprise two layers ofpentagonal tubes of phosphorus with all of the tubes parallel, and thenanother pair of layers of all pentagonal tube phosphorus, the tubes inthe second pair of layers all being parallel, but the tubes in thesecond pair of layers being perpendicular to the tubes in the first pairof layers. The space group of the crystals has been determined, as wellas the bond angles and bond distances. See the summary of the prior artin the section "Phosphorus" from "The Structure of the Elements" byJerry Donahue, published in 1974.

The electronic properties of Hittorf's phosphorus crystals have not beenreported. Because of their small size the electrical properties cannotbe readily determined.

The preparation of high purity electronic grade phosphorus according tothe prior art is very complex and time consuming, thus electronic gradephosphorus is very expen- sive.

The prior art also exhibits a need for stable phosphorus compounds foruse as fire retardants. Crystalline forms have additional utility asreinforcing additives in plastics, glasses and other materials.

DISCLOSURE OF THE INVENTION

We have discovered a family of alkali metal polyphosphide materialspossessing useful semiconductor, optical, and mechanical properties.

Useful Semiconductor Properties

By "polyphosphide" we mean a material dominated by multiplephosphorus-to-phosphorus bonds. By "useful semiconductor" we mean notonly that the conductivity is intermediate between insulators andmetals, but also the demonstration of a host of useful properties:

    ______________________________________                                        Stability                                                                     Resilient material structure                                                  Bandgap in a useful range (typically 1 to 2.5 eV)                             High inherent resistivity, but with ability to be                             doped                                                                         Good photoconductivity                                                        Efficient luminescence                                                        Ability to form a rectifying junction                                         Ability to be formed at relatively low tempera-                               tures (for semiconductors) by processes amenable                              to scale-up                                                                   Ability to be formed as large area amorphous thin                             films                                                                         Ability to be formed as ductile polymeric fibers                              ______________________________________                                    

The polyphosphides are a unique family of materials possessing all ofthese features.

Preservation of Utility in Multiple Forms

It is equally significant that the useful properties remain essentiallyconstant over a wide range of chemical compositions and physical forms(crystalline and amorphous). To our knowledge, polyphosphides are theonly useful semiconductors in which desirable single crystal-likeproperties are preserved in the amorphous form. This is of majortechnological significance because the amorphous form is at the leastmore amendable, and often essential, for large scale applications, suchas photovoltaic cells, large area displays, and electrostatic copiers.

But up to now, the problem with amorphous semiconductors is that they donot form readily as a stable single phase material. And even when theyare forced to, the amorphous form loses some very desirable features ofits crystalline counterpart.

The dominant known semiconductor (silicon) has a tetrahedralcoordination in its crystalline form. Any attempt to make it amorphous(to make amorphous Si) is known to be accompanied by a breaking of thetetrahedral bonds, leaving "dangling bonds" that destroy usefulsemiconducting properties. Pure amorphous Si is useless: unstable andcrumbly. Attempts to satisfy the dangling bonds with Hydrogen orFluorine have been only partially successful.

Central Role of Structure

We believe that the preservation of useful properties among the multipleforms of the polyphosphides are a direct result of the structure of thematerials which, in turn, is made possible by the unique properties ofphosphorus, particularly its ability to form polymers dominated by 3phosphorus to phosphorus covalent bonds at the vast majority ofphosphorus sites.

In the crystalline form, the polyphosphides of the type MP₁₅ (with M=Li,Na, K, Rb, Cs) have a structure formed by a phosphorus skeletonconsisting of parallel tubes with pentagonal cross section. Thesephosphorus tubes are linked by P--M--P bridges shown in FIGS. 4, 5 and6. The building block for this MP₁₅ atomic framework can be viewed as P₈(formed by 2 P₄ rigid units) and MP₇ (formed by the association of MP₃and P₄ rigid units).

Using the building blocks or clusters described above, Kosyakov in areview article (Russian Chemical Review, 48(2), 1979) showedtheoretically that these polyphosphide compounds could be treated aspolymeric materials using their basic building blocks as monomers.Hence, in principle it is possible to construct a large number of atomicframeworks having the same phosphorus skeletons.

In our work, we have synthesized by various techniques described later,MP₁₅ crystals and also compositions of the type [MP₇ ]_(a) [P₈ ]_(b)with b much greater than a. These novel phosphorus rich compoundsoriginally observed as "fibers", "whiskers", or "ribbons" are referredto in this investigation as MP_(x) with x much greater than 15. Theselow metal content materials are prepared by vapor transport as thickfilms (greater than 10 microns) of polycrystalline fibers and largeboules (greater than 1 cm³) of amorphous character. The polycrystallinefibers exhibit the same morphology as KP₁₅ whiskers.

The structural framework of the first MP_(x) (x much greater than 15)crystalline materials we discovered is dominated by a phosphorusskeleton similar to the phosphorus framework of the MP₁₅ compounds.

We have found that the useful electrical and optical properties of thesecrystalline materials MP₁₅ and MP_(x) (x much greater than 15) aresimilar. The properties of these materials are therefore dominated bythe multiple P--P covalent bonds of the phosphorus skeletons with acoordination number somewhat less than 3. To our surprise we have alsodiscovered that the useful electro-optical properties of these materialswere essentially preserved for MP₁₅ and MP_(x) (x much greater than 15)crystalline materials and their amorphous counterparts.

Unlike previously known materials, this is a one dimension rigidstructure and is resilient in the following sense. The polyphosphidecrystal symmetry is very low (triclinic). We believe that in thetransition from the crystal to the amorphous form, the low symmetrymaterial is capable of accommodating in a gradual way the increasedstructural disorder that characterizes the amorphous state. There is noripping apart of strong tetrahedral bonds (coordination number of 4) asin silicon because the phosphorus, with a much lower coordination numberthan silicon, can accept much greater structural disorder without thecreation of dangling bonds. The polyphosphides are polymeric in nature.The result is a polymeric amorphous structure with no apparent X-raydiffraction peaks, one with longer-range local order than is achievablewith conventional amorphous semiconductors. We believe that this gradualonset, in the structural sense, of amorphicity is the reason for thepreservation of the desirable crystal properties in the amorphouspolyphosphides.

Distinguishable from Known, Useful Semiconductors

The composition and structure of the family of polyphosphides clearlydistinguishes them from all known, useful semiconductors:

    ______________________________________                                        Group 4a      (Crystal Si, amorphous Si:H, etc.)                              3a-5a (III-V) (GaAs, GaP, InP, etc.)                                          2b-6a (II-VI) (CdS, CdTe, HgCdTe, etc.)                                       Chalcogenides (As.sub.2 Se.sub.3)                                             1b-3a-6a      (CuInSe.sub.2)                                                  ______________________________________                                    

Distinguishable from Known Forms of Phosphorus

The alkali polyphosphides (MP_(x), M=Li, Na, K, Rb, Cs; where x=15 andmuch greater than 15) are phosphorus rich. In cases of "high x" materialthey are almost all phosphorus. Nonetheless, their structure (parallelpentagonal tubes) and their properties (stability, bandgap,conductivity, photoconductivity) clearly distinguish them from all knownphosphorus materials (black, white/yellow, red, and violet/ Hittorf).The structural relationships among these various forms are discussedbelow.

Our work has done much to clarify this aspect of phosphorus itself. Thenomenclature in this area has been somewhat confusing. The followingsummarizes our current usage.

1. Amorphous P or Red P

Amorphous red phosphorus is a generic term for all non-crystalline formsof red phosphorus, usually prepared by thermal treatment of whitephosphorus.

2. Violet P

This microcrystalline form of red phosphorus is prepared from charges ofpure P, either white or amorphous red, by extended thermal treatment.

3. Hittorf's P

Crystalline form of red phosphorus structurally identical to Violet P.Hittorf's P is prepared in the presence of a large excess of lead.Despite this, the terms "Hittorf's P" and "Violet P" have often beenused interchangeably. The crystal structure consists of double layers ofparallel pentagonal tubes, with adjacent double layers perpendicular toeach other in a monoclinic cell. Hittorf's P crystals are somewhatlarger (approximately 100 microns) than violet P microcrystals.

4. Large Crystal Monoclinic Phosphorus

Even larger crystals (several mm), essentially isostructural with theabove two, are described herein. These novel crystals are prepared byVapor Transport (VT) treatments of alkali-phosphorus charges. Theinclusion of the alkali is apparently essential for formation of thelarge crystals. Analysis confirms the presence of alkali (500 to 2000ppm) in these large crystals of phosphorus.

5. Twisted Fiber Phosphorus

A crystalline form of phosphorus described herein prepared by VTtreatments of amorphous P charges. Believed to be nearly-isostructuralwith polycrystalline MP_(x) "ribbons".

ROLE OF THE METAL: WHY PHOSPHORUS IS NOT GOOD ENOUGH

The many allotropic forms of elemental P are evidence for the varietyand complexity of the bonds and structures that are accessible withphosphorus. We lack a detailed, comprehensive model of exactly how thealkali metal works, but have developed a large and body of data showingthat the metal stabilizes phosphorus so that a single unique structuremay be selected from the ensemble of potentially available structures.

Without at least some alkali metal, the following undesired phenomenaoccur:

A. The phosphorus is unstable (e.g., White P).

B. To the extent that a known single phase is accessible to the P, itcan only do so at high temperatures and of a size limited tomicrocrystals (e.g., Violet P), or

C. At high pressures (e.g., black P).

D. Without an alkali metal in the charge, the MP_(x) type of structureis not formed by vapor transport. Rather, the twisted phosphorus fiberform we have discovered is obtained. This crystalline phase ismetastable and the structure is not well defined as shown by our X-ray,Raman and photoluminescence data.

The presence of alkali metal in vapor transport favors the all-paralleluntwisted phase. It also, as discovered by us, favors large crystals ofmonoclinic P to form at a different temperature.

The dominant role of structure, not composition, as the determinant ofproperties is made clear by noting that KP_(x) (x much greater than 15)has properties (bandgap, photoluminescence, Raman spectra) that areessentially those of KP₁₅, but are somewhat different from those ofmonoclinic P.

It is clear that even a little alkali metal can serve to select a stablephase. But will non-alkalis work? Krebs reported non-alkalipolyphosphides, with tubular structures consisting of 2b-4a-P₁₄ (2b=Zn,Cd, Hg and 4a=Sn, Pb). Why do these form?

A speculative hypothesis is that these materials form in the tubularstructure because the Group 4a element is amphoteric and can occupy a Psite in lieu of P.

One can compute an effective electron affinity of the P₁₅ frameworkbased on the ionization energies of the alkali metals, all of which areless than or equal to 5.1 eV. One can, in turn, calculate effectiveionization potentials for other possible compositions such as the2b-4a-P₁₄ compounds. All of Krebs'materials noted above have "effectiveionization" less than or equal to 4.8 eV.

USEFUL PROPERTIES

Our major initial discovery was that the KP₁₅ whiskers (single crystal)were stable semiconductors, with an energy bandgap corresponding to redlight (1.8 eV) and exhibiting efficient photoconductivity andphotoluminescence. These are the hallmarks of a semiconductor withpotential applications in electronics and optics. Whiskers of the otheralkali MP₁₅ materials also have these properties (M =Li, Na, Rb, Cs).

To realize their potential, the materials had to be prepared in a sizeand form suitable for fabricating devices and for testing. We recognizedthat the crystal habit, however, is not conducive to growth of large,single crystals that are free of crystallographic "twinning". Large,twin-free single crystals are the basis of nearly all semiconductordevice technology today. Polycrystalline materials are less desirablebecause even if the individual grains are large, the presence of grainboundaries serves to destroy some desirable properties due to thephysical and chemical discontinuities that are associated with suchboundaries. Hence, our attention turned to the amorphous forms we haddiscovered.

Useful amorphous semiconductors, whether used as a junction device suchas a photovoltaic cell, or as a coating such as in an electrostaticcopier, have been generally made as thin films for extrinsic reasons(cost, manufacturing ease, and application need) and intrinsic reasons(material problems in the bulk amorphous state).

We have discovered that KP₁₅ can be made as a stable amorphous thin film(by Vapor Transport). (This cannot be done with silicon: amorphous Si isnot stable, while single crystal Si is.)

Stable, bulk, and thin film amorphous KP_(x) (x much greater than 15)can also be made by vapor transport.

There is evidence that these polyphosphides are unusual in yet anotherway. The useful properties of these materials MP₁₅ and MP_(x) (x muchgreater than 15) are similar in their crystalline forms and theiramorphous counterparts as shown in Tables XVI and XVII below.

Applications utilizing amorphous thin film KP₁₅ requiring no junctionscan be readily envisioned (e.g., electrostatic copying). In fact, thehigh inherent resistivity (approximately 10⁸ to 10⁹ ohm-cm) is anadvantage for such junctionless system applications.

Electronic and opto-electronic devices all require that some junction beformed in or with the material to provide a sharp discontinuity in thepotential energy felt by the charge carriers. This requires lowering theresistivity of the material by doping.

We have discovered that Ni diffused into KP₁₅ serves the purpose ofreducing the resistivity of the material by several orders of magnitude.Surface analysis has demonstrated that Ni diffusion from the solid state(KP₁₅ deposited onto a layer of Ni) follows a normal diffusion patternduring the growth process of the film.

Device configurations with Ni as a back contact and diffuser; and othermetals, such as Cu, Al, Mg, Ni, Au, Ag and Ti as top contacts, lead tojunction formation. Junction Current-Voltage (I-V) characteristics havebeen measured with these top contacts. Junction Capacitance- Voltage(CV) characteristics have been measured with Al and Au top contacts. Thedata indicates double junction formation with a high resistance layernear the top contact.

The high resistance layer is an undoped portion of the KP₁₅ film whichresults from the present doping procedure.

A small photovoltaic effect (micro amp current under a short curcuitcondition) has been observed.

SYNTHESIS OF POLYPHOSPHIDES

Below are described the methods we have discovered that will producepolyphosphides of varying composition and morphology.

A. Condensed Phase (CP) Synthesis

This refers to the process of isothermal heat-up, soak (heating at settemperature), and cool down of starting charge carried out in acontainer of minimum volume. There is no vapor transport. Crystallineand bulk polycrystalline are produced.

B. Single Source Vapor Transport Synthesis (1S-VT)

A starting reactant charge is located in one area of an evacuated tubewhich is heated to a temperature, Tc, which is greater than Td, where Tdrepresents the temperature(s) of other area(s) of the tube wherematerials deposit from the vapor. Crystalline MP₁₅ ; crystalline,polycrystalline (bulk, and thin films) and amorphous bulk high x, MP_(x); monoclinic phosphorus; star shaped fiber; and twisted fiber phosphorusare produced.

C. Two Source Vapor Transport Synthesis (2S-VT)

Source reactant charges loaded in an evacuated chamber are separatedphysically by distance with a deposition zone between them. The twosources are heated to temperatures greater than the deposition zone (inorder to get amorphous material, at least; see below). The depositionzone need not be the coldest one in the system, but a colder area shouldnot be able to trap more than one component. 2S-VT was the first methodused to make thin film amorphous KP₁₅. Polycrystalline and amorphousthin films of MP₁₅ and polycrystalline thin films and bulk amorphoushigh x, MP_(x) are produced.

D. Melt Quench

A charge is heated in a sealed evacuated tube (isothermally, ifpossible) to temperatures greater than the "melting point" as determinedby endotherms observed in DTA experiments, and held there for someperiod of time. The tube is then removed from the furnace and rapidlycooled. CsP₇ glass has been produced.

E. Flash Evaporation

A charge in powder form is fed in small amounts, under a slight Argonflow, into an RF-heated susceptor, which is maintained at temperaturesgreater than about 800° C. Inside the susceptor, the material is putthrough a tortuous path where it is, in theory, forced to contact hotsurfaces. This is intended to rapidly and completely vaporize the chargesuch that the composition of the resultant vapor stream is the same asthat of powder being injected. The vapor stream is directed into anevacuated chamber where it strikes cooler surfaces, resulting incondensed-product materials. Amorphous have been produced.

F. Chemical Vapor Deposition (CVD)

In general, this refers to production of material by mixing two (ormore) vaporized components which must undergo some chemical reaction togive products. As practiced by us, K and P₄ are independently meteredint furnaces where they are rapidly vaporized and carried downstream bythe Argon flow to a cooler reaction chamber where the combined streamsyield condensed product materials.

The significance of CVD lies in that of these methods, it is the mostamenable to scale-up and to doping in situ, i.e., simultaneous synthesisand doping of material. Amorphous thin films of KP₁₅ have been produced.

G. Molecular Flow Deposition (MFD)

This is a multi-source vapor transport technique that draws on 2S-VT andMolecular Beam Epitaxy (MBE). Independently heated sources are used andthe vaporized species are allowed to reach the substrate (alsoindependently heated) at a controlled rate not achievable with 2S-VT.The deposition takes place in an evacuated chamber with in situmonitoring of the deposition (also not available with 2S-VT). Thechamber may be sealed or continuously evacuated to control pressure.

KP₁₅ Materials

A large variety of polyphosphide materials of different physical formsand compositions were initially prepared during our investigations.

However, for potential useful semiconductor applications, the emphasisof our work has changed from the preparation of single crystal materialsto that of amorphous materials--either in bulk or large area thin films.

Among all the MP₁₅ materials KP₁₅ is a unique crystalline higherpolyphosphide (x the same as or greater than 7) compound which existsfor the K-P system. (In contrast, the other alkali metals can formcompounds with x =7 or x=11, such as CsP₇, NaP₇, RbP₁₁, etc.). KP₁₁ andKP₇ do not form as compounds. For this reason, the K-P system is easierto control than the other alkali-metal-P systems, where multiplecompounds can form.

In addition, from the results of our experimental work, it is apparentthat whenever K +P are vaporized, by whatever means, and brought in theproper ratio ([P]/[K]the same as or greater than 15) to a zone whosetemperature is in the proper window, amorphous KP₁₅ will form. By thiswindow we mean the temperature must be low enough to preventcrystallization of KP₁₅ and high enough that KP_(x), where x is muchgreater than 15, is not deposited.

Based on this tenet, all synthesis methods can be seen to operate on thesame general principle. Each method simply used different means toachieve control of source vaporization or control of deposition. The twosource systems (2S-VT, CVD and MFD) are particularly useful as theimportant variables can be independently controlled.

Based on the above considerations, KP₁₅ amorphous in thin films has beenselected by us as our leading composition for the development of usefulsemiconductor materials.

SUMMARY

In a general inquiry into the nature of polyphosphides, potassiumpolyphosphide whiskers of about 1 cm in length were produced by singlesource vapor transport. In investigating the properties of this materialit was determined by x-ray diffraction of a single crystal that thecrystals were KP₁₅. It was also discovered that these crystals weresemiconductors. When measuring an emission at 4° K. under argon laserillumination, photoluminescence was observed having an energy of 1.8 eV,thus indicating that the material possibly had a band gap within thisenergy range.

Later, in order to determine the conductivity of these whiskers, leadswere attached with silver paint. In order to see if the leads wereactually attached to a very small crystal, it was placed under amicroscope while the conductivity was measured. Surprisingly theconductivity changed dramatically when the crystal was moved in themicroscope, changing the illumination. A photoconductivity ratio of 100was measured with the unilluminated conductivity of the whisker beingabout 10⁻⁸ (ohm-cm)⁻¹. To establish whether the whiskers had a band gap,measurements were then made of the wavelength dependence of thephotoconductivity, the wavelength dependence of the optical absorptionand the temperature dependence of the conductivity of the whisker. Thesemeasurements, together with the photoluminescence measurement at 4° K.,established that the whiskers had a band gap of approximately 1.8 eV.Thus it was established that KP₁₅ crystalline whiskers were potentiallyuseful semiconductors.

An amorphous film was formed on the inside of the quartz tube during thevapor transport production of the KP₁₅ whiskers. This amorphous film wasalso found to have a band gap on the order of 1.8 eV and aphotoconductivity ratio on the order of about 100. Like the whiskers,the amorphous film had an electrical conductivity of approximately 10³¹8 (ohm-cm)⁻¹. Thus it was established that it also was a potentiallyuseful semiconductor.

The problem then presented to the inventors was whether KP₁₅ could beproduced as large crystals, such as silicon, used in semiconductorproduction; whether polycrystalline or amorphous films of KP₁₅ could bereproducibly made and utilized for semiconductor production; and thefull charaterization of the materials produced by the vapor transportexperiment and any analogous materials which might have the same usefulproperties.

After many vapor transport experiments the inventors were astonished tofind that the polycrystalline and amorphous materials that were producedby vapor transport where a single source of a mixture of potassium andphosphorus is heated and material condensed at the other end of a closedtube, were not KP₁₅ but when measured by wet analysis were KP_(x) wherex seemed to range from about 200 to about 10,000.

The inventors have since made the amazing discovery that the affinity ofphosphorus for potassium, or any alkali metal for that matter, in singlesource vapor transport causes initial deposition of MP₁₅ as the moststable polyphosphide. If there is an excess of phosphorus, then a newform of phosphorus will be deposited. (MP_(x) where x is much greaterthan 15) This new form of phosphorus has the same electronic qualitiesas KP₁₅ and is a useful semiconductor.

During the course of their investigations the inventors, in an effort toform thin films of polycrystalline and amorphous KP₁₅ and other alkalimetal analogs which could not be formed by single source vaportransport, conceived of a two source (separated source) vapor transportmethod in which the alkali metal and the phosphorus are spaced apart andseparately heated. By controlling the temperature of a separateintermediate deposition zone, thin films of MP₁₅ where M is an alkalimetal, have been made in polycrystalline and amorphous forms. Thistechnique has also led to the production of thin films ofpolycrystalline and thick films of amorphous phosphorus material of thenew form, and other materials presumably polymer-like having the formulaMP_(x), where M is an alkali metal and x is much greater than 15.

We have also used Flash Evaporation, Chemical Vapor Deposition, andpropose to use Molecular Flow Deposition methods for synthesizing thesematerials.

We use MP_(x) as the formula for all polyphosphides. As will be pointedout below, for useful semiconductors, x may range from 7 to infinity.Known alkali polyphosphides have the formula MP₇, MP₁₁, and MP₁₅. Wehave discovered that presumably polymer forms exist having the formulaMP_(x) where x is much greater than 15.

Also during these investigations single source vapor transport has beenimproved over the prior art by controlling the deposition temperature tobe constant over a large area, so that large area thick films and boulesof polycrystalline and amorphous MP_(x) where x is much greater than 15have been formed.

Large quantities of crystalline and polycrystalline MP₁₅, where M is analkali metal, have been made by heating together isothermallystoichiometric proportions of an alkali metal and phosphorus. Thiscondensed phase method produces excellent MP_(x) where x ranges from 7to 15 for use in single source vapor transport. The condensed phasemethod itself is facilitated by the prior mixing and grinding togetheran alkali metal and phosphorus in a ball mill which is preferably heatedto a temperature in the neighborhood of 100° C. This ball millingsurprisingly produces relatively stable powders.

All of the parallel tube polyphosphides have a band gap of approximately1.8 eV, photoconductivity ratios much greater than 5, (measured ratioshaving a range from 100 to 10,000), and low conductivity in the order of10⁻⁸ to 10⁹ (ohm-cm)⁻¹.

Since we have discovered that the amorphous forms of these materials,i.e. alkali polyphosphides MP_(x) where x is greater than 6 formed inthe presence of an alkali metal have substantially the samesemiconductive properties, we conclude that the local order of theamorphous materials is the same all parallel pentagonal tubessubstantially throughout their extent.

In all the polyphosphides, the 3 phosphorus-to-phosphorus (homatomic)covalent bonds at the majority of phosphorus sites dominate any otherbonds present to provide the conduction paths and they all havesemiconductor properties.

The covalent bonds of the phosphorus atoms all of which are used in thecatenation providing the dominant conduction paths and the parallellocal order in these materials provide the good semiconductingproperties. The phosphorus atoms are trivalent and the catenations formspirals or tubes having channel-like cross sections. The alkali metalatoms, when present, join the catenations together. Atomic species otherthan phosphorus, particularly trivalent species capable of forming 3covalent homatomic bonds, should also form semiconductors.

Thus we have invented new forms of phosphorus and methods of making thesame, solid films of amorphous and polycrystalline MP_(x) and methodsand apparatus for making the same, methods and apparatus for makingmetal polyphosphides by multiple temperature single source techniques,methods and apparatus for making high phosphorus polyphosphides bymultiple separated source techniques, methods and apparatus for makingMP₁₅ by condensed phase techniques in polycrystalline forms,semiconductor devices comprising polyphosphide groups of seven or morephosphorus atoms covalently bonded together in pentagonal tubes having aband gap greater than 1 eV and photoconductivity ratios of 100 to10,000, semiconductor devices comprisihg MP_(x) where M is an alkalimetal and x is greater than 6, and materials having a band gap greaterthan 1 eV and photoconductivity ratios of 100 to 10,000, semiconductordevices formed of a high proportion of catenated covalently bondedtrivalent atoms preferably phosphorus where the catenated atoms arejoined together in multiple covalent bonds the local order of whichcomprises layers of catenated atoms which are parallel in each layer andthe layers are parallel to each other, the catenations preferably beingpentagonal tubes, semiconductor devices comprising an alkali metal andsaid catenated structures wherein the number of consecutive covalentcatenated bonds is sufficiently greater than the number of non-catenatedbonds to render such material semiconducting, semiconductor devicesformed of compounds comprising at least two catenated units, each unithaving a skeleton of at least 7 covalently bonded catenated atomspreferably phosphorus and having alkali metal atoms conductivelybridging the skeleton of one unit to another, junction devices, methodsof forming such semiconductor devices, methods of doping suchsemiconductor devices, methods of conducting electrical current andgenerating electrical potential utilizing such devices.

We have therefore discovered a whole class of materials to be usefulsemiconductors, some members of the class having been first produced orproperly characterized by us, and others of which have been produced inthe prior art with their useful semiconductor properties being unknownuntil our discoveries and inventions.

All of these materials have a band gap within the range of 1 to 3 eV,preferably within the range of 1.4 to 2.2 eV and most preferably about1.8 eV. Their photoconductivity ratios are greater than 5 and actuallyrange between 100 and 10,000. Their conductivities are within the rangeof 10⁻⁵ 10⁻¹² (ohm-cm)⁻¹, being in the order of 10⁻⁸ (ohm-cm)⁻¹.

Those skilled in the art will readily understand that the alkali metalcomponent M of polyphosphide or any appropriate trivalent "ide" capableof forming homatomic covalent bonds, and having the formula MY_(x) maycomprise any number of alkali metals, (or combination of metalsmimicking the bonding behavior of an alkali metal) in any proportion,without changing the basic pentagonal tubular structure and thus withoutsignificantly affecting the electronic semiconductor properties of thematerial.

We have further discovered and invented methods of doping the materialsof the invention utilizing doping with iron, chromium and nickel, toincrease the conductivity. Junctions have been prepared using Al, Au,Cu, Mg, Ni, Ag, Ti, wet silver paint, and point pressure contacts.

The incorporation of arsenic into the polyphosphides (all paralleltubes) has also been demonstrated to increase conductivity.

These doping methods are also part of our invention and discovery.

The semiconductor materials and devices of the present invention have awide variety of uses. These include photoconductors such as inphotocopying equipment; light emitting diodes; transistors, diodes andintegrated circuits; photovoltaic applications; metal oxidesemiconductors; light detection applications; phosphors subjected tophoton or electron excitation; and any other appropriate semiconductorapplication.

In the course of our work we have also produced for the first time largecrystals of monoclinic phosphorus. These crystals are obtained fromvapor transport technique using MP₁₅ charge or mixture of M and P (M/P)in varying ratios. Surprisingly, these large crystals of monoclinicphosphorus contain a significant amount of alkali metals (500 to 2000ppm have been observed). Under the same conditions, these crystalscannot be grown without the presence of alkali metals in the charge.

Two different crystal habits have been observed for these large crystalsof phosphorus.

One crystal habit was identified as truncated pyramidal shape crystalsas shown in FIG. 39. These cyrstals are hard to cleave. The other formis a platelet-like crystal and is cleavable as shown in FIG. 40.

The largest crystals we have produced in the habit shown in FIG. 39 are4×3 mm×2 mm high. The largest crystals we have produced in the habitshown in FIG. 40 are 4 mm square and 2 mm thick.

The crystals are metallic looking on reflection and deep red intransmission. Chemical analysis indicates that they contain anywherefrom 500 to 2000 parts per million of alkali metal. Their powder X-raydiffraction patterns, Raman spectra and differential thermal analysisare all consistent with the prior art Hittorf's phosphorus.

Photoluminescence of crystals grown in the presence of Cesium in FIG. 41and crystals grown in the presence of Rubidium in FIG. 42 show peaks at4019 and 3981 cm⁻¹, which indicate a band gap of about 2.1 eV at roomtemperature for this monoclinic phosphorus.

The crystals may be utilized as a source of phosphorus; as opticalrotators in the red and infra-red portion of the spectrum (they arebirefringent); as substrates for the growth of 3-5 materials such anIndium Phosphide and Gallium Phosphide. They may be utilized inluminescent displays or as lasers.

We have grown from the same charge and deposited at a slightly lowertemperature the star shaped fibrous crystals shown in FIGS. 44 and 45.

We have also grown by vapor transport a crystal allotrope of phosphorus,the twisted fiber of phosphorus shown in FIG. 46.

The polyphosphides may be used as fire retardants and strengtheningfillers in plastics, glasses and other materials. The twisted tube andstar shaped fibers should be of particular value in strengtheningcomposite materials because of their ability to mechanically interlockwith the surrounding material. The platelets should be of particularvalue in thin sheet material where glass flakes are now employed.

The film materials of the invention may be utilized as coatings fortheir chemical stability, fire retardant and optical properties.

OBJECTS OF THE INVENTION

It is therefore an object of the invention to provide a new class ofuseful semiconductor materials.

Other objects of the invention are to provide new methods and apparatusfor making polyphosphides.

Still other objects of the invention are to provide new forms of stablehigh phosphorus materials and methods and apparatus for making the same.

Further objects of the invention are to provide new forms of phosphorusand methods and apparatus for making the same.

Still other objects of the invention are to provide dopants and methodsof doping such materials.

Yet other objects of the invention are to provide semiconductor devicesemploying the above.

Another object of the invention to provide large crystals of monoclinicphosphorus.

Still another object of the invention is to provide high purityphosphorus.

Still another object of the invention is to provide new semiconductormaterials.

Still another object of the invention is to provide a birefringentmaterial for use in the red and infra-red portion of the spectrum.

Yet still another object of the invention is to provide methods formaking materials of the above character.

A further object of the invention is to provide such methods which aremore convenient than the prior art and less expensive.

Other objects of the invention are to provide coating materials,fillers, reinforcing materials and fire retardants.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises one or more inventive steps and therelation of such steps with respect to each of the others which will beexemplified in the methods and processes hereinafter described,compositions of matter possessing the characteristics, properties andthe relationship of constituents and components which will beexemplified in the compositions hereinafter described, articles ofmanufacture possessing the features, properties, and the relation ofelements which will be exemplified in the articles hereinafter describedand apparatus comprising the features of construction and arrangement ofparts which will be exemplified in the apparatus hereinafter described.The scope of the invention is indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description, taken inconnection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic view partly in cross section of single sourcevapor transport apparatus according to the invention;

FIG. 2 is a diagrammatic view of a portion of the vapor transportapparatus of FIG. 1;

FIG. 3 is a diagrammatic view of another single source vapor transportapparatus according to the invention;

FIG. 4 is a computer diagram from X-ray diffraction data of phosphorusatoms in where MP₁₅ is an alkali metal;

FIG. 5 is a computer diagram from X-ray diffraction data of a crosssection of KP₁₅ showing how the covalent bonding of the phosphorus atomsof FIG. 4 forms a pentagonal tubular structure;

FIG. 6 is a computer diagram from X-ray diffraction data in longitudinalsection of KP₁₅ ;

FIGS. 7 and 8 are photomicrographs of KP₁₅ crystal whiskers;

FIG. 9 is a powder X-ray diffraction fingerprint of crystalline KP₁₅ ;

FIG. 10 is a powder X-ray diffraction fingerprint of crystalline KP_(x)where x is much greater than 15;

FIG. 11 is a diagrammatic view of an experimental reaction tube for twosource vapor transport according to the invention;

FIG. 12 is a plot of temperature versus length for the reaction tube ofFIG. 11;

FIG. 13 is a diagram of the P to K ratio of the reaction products in thereaction tube of FIG. 11;

FIG. 14 is a schematic diagram of apparatus for a two source vaportransport according to the invention;

FIG. 15 is a diagram of one of the elements of the apparatus illustratedin FIG. 14;

FIG. 16 is a diagrammatic view of another reaction tube for two sourcevapor transport according to the invention;

FIG. 17 is a diagrammatic view of a ball mill according to theinvention;

FIGS. 18, 19 and 20 are scanning electron micrographs (SEM's) of a filmof a new form of phosphorus MP_(x) where x is much greater than 15;

FIG. 21 is a photomicrograph of an etched amorphous surface of such highx MP_(x) synthesized by single source vapor transport according to theinvention;

FIG. 22 is an photomicrograph of an etched amorphous surface of suchhigh x MP_(x) synthesized by two source vapor transport according to theinvention;

FIG. 23 is an photomicrograph of the same surface as shown in FIG. 22;

FIG. 24 is an photomicrograph of an etched surface perpendicular to thesurface shown in FIGS. 22 and 23;

FIG. 25 is an SEM photomicrograph of the upper surface of an amorphousthin film of KP₁₅ synthesized by two source vapor transport according tothe invention;

FIG. 26 is a cross sectional view partly in diagrammatic formillustrating the formation of a junction according to the invention;

FIG. 27 is an illustration of the oscilloscope screen in the experimentillustrated in FIG. 26; and

FIG. 28 is a cross sectional view partly in diagrammatic formillustrating the formation of a junction according to the invention;

FIG. 29 is an illustration of the oscilloscope screen in the experimentillustrated in FIG. 28;

FIG. 30 is a diagram of a photosensitive resistor according to theinvention;

FIGS. 31, 32, and 33 are illustrations of oscilloscope screens showingjunction activity in devices according to the invention;

FIGS. 34, 35 and 36 are plots of capacitance versus applied electricalpotential in function devices according to the invention;

FIG. 37 is a plot of capacitance and resistance as a function offrequency of applied potential of devices according to the invention;

FIG. 38 is a diagram of a preferred form of sealed ampoule utilized toform monoclinic phosphorus according to the invention;

FIG. 39 is a photomicrograph of a crystal of monoclinic phosphorusaccording to the invention;

FIG. 40 is a photomicrograph of a crystal of monoclinic phosphorusaccording to the invention;

FIG. 41 is a diagram of the photoluminescence response of a crystal ofmonoclinic phosphorus according to the invention;

FIG. 42 is a diagram similar to FIG. 6 of the photoluminescent responseof a crystal of monoclinic phosphorus according to the invention; and

FIG. 43 is a Raman spectrum of monoclinic phosphorus according to theinvention.

FIG. 44 and 45 are SEM photomicrographs of another new form ofphosphorus according to the invention;

FIG. 46 is an SEM photomicrograph of still another new form ofphosphorus according to the invention;

FIG. 47 is a side diagrammatic view of flash evaporation apparatusaccording to the invention;

FIG. 48 is a cross sectional view taken along the line 48--48 of FIG.47;

FIG. 49 is a cross sectional view taken along the line 49--49 of FIG.48; and,

FIG. 50 is a diagram of chemical vapor deposition apparatus, accordingto the invention.

The same reference numbers refer to the same elements throughout theseveral views of the drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

The high phosphorus materials of the invention exemplified by the highphosphorus polyphosphides MP₁₅ where M is an alkali metal, and the newforms of phosphorus formed, are all believed to have similar localorder, whether crystalline, polycrystalline or amorphous. We believethat in both crystalline and amorphous MP₁₅, this local order takes theform of elongated phosphorus tubes having pentagonal cross sections asshown in FIGS. 4, 5 and 6. All of the pentagonal tubes are generallyparallel on the local scale and in MP₁₅ double layers of the pentagonalphosphorus tubes are connected to each other by interstitial alkalimetal atoms. In the new forms of phosphorus of our invention, many, ifnot most of the alkali metal atoms are missing. However, it appears thatone new form of phosphorus formed in the presence of very small amountsof alkali metal atoms grows from vapor deposition in the same form asMP₁₅. One experiment to be discussed below indicates that at least oneform of this is by growth of the new form of phosphorus on a layer ofMP₁₅. The MP₁₅ may act as a template causing the phosphorus to organizein the same structure. All of the materials having these all parallelpentagonal phosphorus tubes have been found by us to have a band gapbetween 1.4 and 2.2 eV and most on the order of 1.8 eV.Photoconductivity ratios range from 100 to 10,000. Thus it is indicatedthat all high phosphorus alkali metal polyphosphides from MP₇ throughMP₁₅ and more complex forms and mixed polymers of MP₁₅ and the new formof phosphorus discovered by us (MP_(x) where x is much greater than 15),which all have the all parallel pentagonal tube structure, if stable,will be useful semiconductor materials, barring the inclusion ofelements that would act as traps, cause the formation of grainboundaries, or the like.

In all of these materials having the all parallel pentagonal tubularstructure, our investigations indicate that the multiple continuouscovalent phosphorus-to-phosphorus bonds of the tubes being substantiallygreater in number than the number of other bonds will provide primaryelectrical conduction paths for electrons and holes and thus providegood semiconductor properties. It is further our opinion that thepresence of alkali metals in the charge, even when resulting in traceamounts in the new forms of phosphorus we have discovered, promotegrowth of the materials in forms that maintain the same structural andelectronic properties as KP₁₅ or as monoclinic phosphorus, depending ondeposition conditions.

The family of semiconductor members to which the subject invention isdirected comprises high phosphorus polyphosphides having the formulaMP_(x) wherein M is a Group 1a alkali metal, and x is the atomic ratioof phosphorus-to-metal atoms, x being at least 7. Metallic elements ofGroup la most suitable are Li, Na, K, Rb, and Cs. Although franciumpresumably is suitable, it is rare, has not been involved in any knownsynthesis of MP_(x) and is radioactive. High phosphorus polyphosphideswhere M includes Li, Na, K, Rb or Cs have been formed and tested by theinventors.

The polyphosphide compounds of this invention as presently defined mustcontain an alkali metal. Some of the new forms of phosphorus must beformed in the presence of minor amounts if not unmeasurable amounts ofalkali metal. However, other metals may be present in minor amounts as,for example, dopants or impurities.

KP₁₅ and, as we later learned, a new form of phosphorus was firstsynthesized as follows.

Referring to FIG. 1, a two temperature zone furnace 10 comprises anouter sleeve 12 preferably constructed of iron. Outer sleeve 12 iswrapped in a thermally insulative coating 14 which can comprise anasbestos cloth. The furnace was constructed in the laboratory shop ofthe inventors.

We used a P/K mole ratio of about twelve (12) as reactants 36 in furnace10. As one illustrative example 5.5 g of rcd phosphorus and 0.6 g ofpotassium were transferred under nitrogen to quartz tube 32. Prior totransfer, the phosphorus was washed repeatedly with acetone, and airdried. However, this washing is considered optional, as is the solventselected.

After being charged with reactants 36, tube 32 was evacuated to, forexample, 10⁻⁴ Torr, sealed, and then placed in furnace 10. Tube 32 wasmounted at a slight incline in the furnace. Power supplied to conductors24 and 26 was adjusted to establish a temperature gradient of, forexample, 650° C. to 300° C. from heat zone 28 to heat zone 30. With theabove described inclination of furnace 10, reactants 36 were assured ofbeing located in the hotter temperature heat zone 28.

After maintaining furnace 10 at these conditions for a sufficient periodof time, for example approximately 42 hours, power to conductors 24 and26 was terminated and tube 32 was allowed to cool. Upon reaching ambienttemperature, tube 32 was cut open under a nitrogen atmosphere and thecontents of tube 32 were removed. The contents were washed with CS₂ toremove pyrophoric materials, leaving approximately 2.0 g of stableproduct. This resulted in a yield of approximately 33 percent.

Using this form of synthesis, various phases of resultant product occurat well defined positions within tube 32 as illustrated in FIG. 2. Adark gray-black residue 40 coupled with a yellow-brown film 42 istypically produced at the extreme end of hot zone 30, where reactants 36are initially located. Moving in a direction of decreasing temperaturealong tube 32, there is next found black to purple film deposits 42which are a polycrystalline material. Next to film deposits 42 is anabrupt dark ring of massed crystallites 44 and immediately adjacentcrystallites 44 is a clear zone wherein whiskers 46 are grown. A highlyreflective coating or film deposit 48 is found on the lower portion oftube 32 in the beginning of cold zone 28. Above film deposit 48 a deepred film deposit 50 occasionally occurs depending on the temperaturemaintained in the zone. The deposits 48 and 50 can be polycrystalline,amorphous or a mixture of polycrystalline and amorphous materialdepending on the reactants and temperature. At the extreme end of coldzone 28 is a mass or film deposit 52 which is amorphous material.

Since there is a continuous temperature gradient from the hot zone tothe cold zone of the reaction tube shown in FIGS. 1 and 2, the nature ofthe materials deposited actually varies continuously from high qualitycrystalline whiskers to polycrystalline to amorphous. In order tomanipulate the reaction and attempt to deposit large areas of uniformlayers of material a three zone furnace was constructed and isillustrated in FIG. 3. As herein embodied, the three zone furnace 54 isessentially identical to furnace 10 illustrated in FIG. 1, in thatfurnace 54 comprises an outer iron sleeve 56, a tube 60, and a reactiontube 58. For purposes of simplicity, asbestos wrappings of outer sleeve56 and tube 58 have been omitted from FIG. 3. Furnace 54 is primarilydistinguishable from furnace 10 in that tube 58 is much longer incomparison to tube 32, and is preferably on the order of 48 cm inlength. In addition, furnace 54 has associated with it three distinctheat zones, 62, 64 and 66 which are individually controllable to createa more definitive heat gradient along tube 60. Tube 60 may be supportedby asbestos blocks 68 and 70 in a manner so as to provide for aninclination of tube 60 and reaction tube 58 toward heat zone 62, inorder to keep reactants 36 in proper position.

Very good quality preparation of KP₁₅ whiskers were obtained usingtemperature set points of 550, 475, and 400 degrees centigrade in heatzones 62, 64 and 66 respectively. It was also found that bulky depositsgenerated in furnace 10, when loaded into inner sleeve 60 of furnace 54and reheated in the above-identified temperature gradient, would sublimeto form film deposits like those of films 48-52 illustrated in FIG. 2,but only when a high zone temperature of at least 400°-475° C. was used.

Unit cell structural information on KP₁₅ crystals produced in accordancewith the method described above was obtained by single crystal X-raydiffraction data, and collected with an automated diffractometer. Afibrous single crystal of 100 microns diameter was selected and mountedon a glass fiber. The structure was determined by direct methods using atotal of 2,544 independent reflections. All the atoms were located by anelectron map and differential Fourier synthesis.

Typical needle-like crystals were examined by high magnification andscanning electronic microscopy (SEM). The resultant SEM photographs ofthe cross section of the needles show that the needles are apparentlycomposed of dense fibrils rather than hollow tubes. Marked twinning ofthe whisker crystals is also discernible on the microphotographs of KP₁₅whiskers in FIGS. 7 and 8. The diameter of the primary fibrils of thewhisker-type crystals is estimated to be approximately 0.1-0.2 microns.Larger fibrils seem to have a fine structure consisting of parallellamellae of approximately 500 angstroms thickness.

From the initial crystal data refinement study, the stoichiometry of thestudied potassium phosphide compound appears to be KP₁₅.

The phosphorus atomic framework of the compound is formed of identicalunit tubes with a pentagonal cross section. The tubes are unidimensionalalong the needle axis direction. The phosphorus tubes are parallel toone another. In the simplest description, double layers of separatedphosphorus tubes are connected by a layer of potassium atoms. As judgedby the inter atomic distances, the K atoms are at least partiallyionically bonded to P atoms. A cross sectional view of a whisker ispresented in FIG. 5.

More specifically, each potassium site is associated with a rigid unitof 15 consecutive phosphorus atoms having a structure as illustrated inFIG. 4. In this rigid unit all the phosphorus atoms but one are bound tothree other phosphorus atoms. The other phosphorus atoms are chainedwith the missing bonds linked to a potassium atom as shown in FIG. 5.Thus, the potassium atom appears to link tubular phosphorus unitsthrough a missing P--P bridge. In the investigated structure, potassiumhas phosphorus atoms as nearest neighbors at distances of 3.6Å, 2.99Åand 2.76Å, respectively. The P--P distances vary from 2.13Å to 2.58Å.The bond angles at the phosphorus chains vary between 87° to 113° andaverage 102°.

Arsenic forms a layered structure having an average bonding angle of 98°and this is not known to be a useful semiconductor. Black phosphorus hasa similar structure and an average bonding angle of 96°. Trivalent atomswhich can form their three bonds within the range of 87° to 113° withthe average above 98° may form the same catenated structure as MP_(x).If the bonds are covalent the material can be expected to have the sameelectronic properties as MP_(x).

Table I gives the crystal lattice parameters and atomic positions wefound for crystalline KP₁₅.

                  TABLE I                                                         ______________________________________                                        Crystal Lattice Parameters For KP.sub.15                                      ______________________________________                                                 Triclinic system                                                              Unit cell parameters                                                          a =  9.087 Å (±0.15) Å                                             b =  11.912 Å (±0.10) Å                                            c =  7.172 Å (±0.15) Å                                             α=                                                                           101.4 (±0.1)°                                                  β=                                                                            107.9 (±0.2)°                                                  γ=                                                                           89.3 (±0.1)°                                          ______________________________________                                    

The unit cell is primitive with one molecule per unit cell and a volumeof 723.3 Cubic Angstroms.

Space group P₁

The highest attainable symmetry in the above structural configuration isa centrosymmetric P₁ space group with the stoichiometry given by KP₁₅.

The corresponding X-ray powder diffraction data for KP₁₅ polycrystallinematerial with copper illumination is shown in FIG. 9. This shows the dspacing with the corresponding X-ray intensities.

Similar X-ray powder diffraction data have been observed for whiskersand polycrystalline MP₁₅ materials with

M=Li, Na, K, Rb and Cs.

In all these isostructural compounds, the structural framework can beviewed as formed of parallel pentagonal phosphorus tubes. These tubesare linked by a P--M--P bridge.

The rigid units for this type of structure are P₄ and MP₃. The buildingblock for the atomic framework can be viewed as [P₄ -MP₃ ] or [MP₇ ].

Therefore:

    [MP.sub.7 ]+2[P.sub.4 ]→[P.sub.4 -MP.sub.7 -P.sub.4 9

which represents the basic structure MP₁₅.

Of course, one of the building blocks in such compounds may be presentin much larger quantities than the other. In the case of MP_(x), forexample, there may exist building blocks of [MP₇ ]and [P₈ ], which arepresent in a ratio of a to b, respectively. In such a case MP_(x) couldbe expressed in the form [MP₇ ]_(a) [P₈ ]_(b), wherein mathematicallyx=(7a+8]b)/(a).

It is also possible for a compound to have b much greater than a andhave the same basic structural framework.

This type of polymer like tubular structure will result in "fibers" orwhiskers of the type MP_(x) with x much greater than 15.

Whiskers and polycrystalline "fibers" of the type MP_(x) with x greaterthan 1000 (M=Li, Na, K, Rb, Cs) have been observed to crystallize at lowtemperature (about 400° C.) using the vapor transport technique. TheX-ray powder diffraction data of these materials are substantially thesame. Data for KP_(x) where x is much greater than 15 under copperillumination is shown in FIG. 10.

We can compare the structure deecribed above to other structures basedon pentagonal cross section phosporus tubes. The KP₁₅ compound is isstructural to LiP₁₅, NaP₁₅, RbP₁₅, CsP₁₅. The other allkali metalsappear to paly the same role as K.

From structural data we concluded that numerous compounds can be formedwhich will be based on pentagonal cross setion tubular building blocks.We also found that in phosophorous materials, at least partially, thephosporous atoms can be replaced by other pnictides, such as As, Bi orSb. Substitution under 50 atom percent is possible, without adverselyaffecting the basic structure of the high phosphorus polyphosphides.

Table II shown the various MP_(x) compounds synthesized that we havefound the same structure as crystalline KP₁₅ as shown by XRD powderdiffraction fingerprint analysis.

                  TABLE II                                                        ______________________________________                                        Rigid units     MP.sub.3 and P.sub.4                                          Building blocks [P.sub.4 --MP.sub.3 ] or [MP.sub.7 ] and [P.sub.8 ]           Basic structure [P.sub.4 --MP.sub.7 --P.sub.4 ] or [MP.sub.15 ]               M:              Li, Na, K, Rb, Cs                                             Compounds Isostructural With Crystalline KP.sub.15                            M.sub.x M'.sub.1-x P'.sub.y P.sub.15-y                                                   with:                                                                              0 ≦ x ≦ 1                                                       y < 7.5                                                               M and M' from Group 1a                                                        P' from Group 5a (As, Bi, Sb)                                         ______________________________________                                    

Initially the inventors found, as previously stated, that thecrystalline whiskers produced in the apparatus of FIGS. 1, 2 and 3 wereMP₁₅. However, analysis of the polycrystalline and amorphous materials,although indicating that these materials had the same semiconductingproperties as the MP₁₅ whiskers, had widely variable stoichiometricproportions from to MP₂₀₀ to MP₁₀,000, and suprisingly no manipulationof the temperatures in the three zone furnace illustrated in FIG. 3would produce amorphous forms of MP₁₅. It was therefore necessary togreatly refine the methods of producing these materials and to invent anew two source vapor transport apparatus in order to successfullyproduce polycrystalline and amorphous MP₁₅ materials. The very high xmaterials which are now thought to be a new form of phosphorus, havealso been prepared by this method by initially depositing MP₁₅ andthereafter cutting off the source of alkali metal so that onlyphosphorus vapor is present for deposition of phosphorus. Additionally,condensed phase process has been extensively investigated in which molarcharges of MP_(x) materials where x varies from 7 to 15 has beeninvestigated. In this method the stoichiometric mixtures are heatedisothermally to reaction and then cooled. We have produced a widevariety of MP_(x) materials in this manner which are crystalline orpolycrystalline powders.

There follows a detailed description of the methods we have employed tosynthesize high phosphorus matrrials and how we have measured theelectro-optical characteristics and demonstrated that they are usefulsemiconductors.

Preparation of Stable High Phosphorus Materials by the Vapor TransportTechnique from a Single Source

Introduction

The technique of applying sufficient energy to a system to create vaporspecies which yield products on condensation or deposition, atappropriate temperatures is called "vapor transport". For the followingdiscussion, where the source materials are held in close contact andheated together at about the same temperature, the further descriptionas a "single source" technique is applicable.

The methodology described by Von Schnering was essentially asingle-source vapor transport technique, although the charge sometimesconsisted of separate ampoules of metal and phosphorus heated to nearlythe same temperatures. However, the flow of vapor species to thedeposition zones was effectively the same as when the metal and thephosphorus are first mixed together. More specifically, in single sourcevapor transport the vapor species are first brought together at a hightemperature and then are deposited at a lower temperature.

The following indicates our development of the technique as it has beenapplied to the preparation of alkali metal polyphosphides and thedeparture from von Schnering's method, which results in improved, moreselective preparation of: crystalline metal polyphosphides of the typeKP₁₅ ; low alkali-metal content polyphosphides, polycrystallinematerial, of the type KP_(x), where x is much greater than 15; and a newform of amorphous phosphorus, in which the alkalimetal content can beless than 50 ppm. (parts per million)

The inventions we have made fall into several categories: type ofcharge, charge ratio, tube length and geometry, and temperature gradientprofile. The following examples illustrate the temperature dependentproduct deposition relationships we have discovered and our improvedtemperature controlling methods that result in the selective preparationof desired products.

General Methods

An alkali metal and red phosphorus are sealed in quartz tubes, atreduced pressures (about 10⁻⁴ Torr). Atom ratios of the two elementsrange from P/M=5/1 to 30/1, with 15 to 1 as the most common charge. Theelements are generally ball-milled together, prior to loading in thequartz tubes. The millings are carried out with stainless steel ballsand mills and last for at least 40 hours. The mills are usually heatedto 100° C. for the duration of the milling, to assist in the dispersionof the metal in the red phosphorus powder.

The milling achieves an intimate contact of the two elements in ashomogeneous a manner as possible. The products of the milling aregenerally fine powders which are easily manipulated in a dry box and maybe stored with little noticeable deterioration. The powders showremarkable stability when exposed to air and moisture, compared to thestability of their constituents, especially the alkali metals. Forinstance, direct addition of water to the powders only results incombustion of materials in random cases and on a small scale.

Preparation of MP₁₅ single crystals, polycrystalline and amorphous

A mixture of the elements (alkali metal and red phosphorus) is sealed atreduced pressure (less than 10⁻⁴ Torr) in a quartz tube 58 (FIG. 3),about 50 cm long by 2.5 cm in diameter. Tube 58 is supported inside theheating chamber of a Lindberg Model 24357 3-zone furnace in one of twoways. One method employs a second quartz tube 60 as a support piece,which is, in turn, held in the chamber, away from the heating elements,by asbestos blocks 68 and 70, such that the coupled tubes rest at anincline, insuring the reactants remain in the hottest zone. The othermethod (FIG. 14) is to use supports built of woven tape 136 wrappedabout the reaction tube in an expanding spiral, an inch wide, andfilling the circular cross section of the heating chamber. This woventape may be made of a variety of materials: Asbestos, Fiberfrax (fromCarborundum Company), or woven-glass. The latter is preferred primarilyon safety and performance criteria. The implications of using the twodifferent methods are described below.

The reactants are driven to products by applying energy to the systemvia the resistance elements of the furnace. If a sufficiently hightemperature is applied to the reactants, while other portions of thetube are held at appropriate lower temperatures, products will deposit,or condense, from vapor species. The temperature differential whichdrives this so-called "vapor-transport" synthesis, is achieved in a3-zone furnace by selecting different setpoint temperatures for theindividually controlled heating elements.

METHOD 1. See FIG. 3. The 50 cm tube, containing the reactants is heldby the second quartz tube in the 61 cm long heating chamber. Applicationof a thermal gradient by manipulation of the 3 set-points results in agenerally linearly-falling gradient. That is, the slope of the gradient,ΔT/d, where T is temperature and d is distance along the chamber, isapproximately constant between the centers of the two outside heatingelements. This linear gradient, applied over the long dimensions of thetube, functions to cleanly separate the variety of product materialsformed in the reaction. The products occur in a characteristic patternof decreasing temperature of deposition: dark purple to blackpolycrystalline films; a ring of massed crystallites; "single" crystalsor whiskers; red films of small-grain, polycrystalline morphology; and,at coldest temperatures, dark grey amorphous material.

A series of experiments have shown that the amorphous material will notform in these sealed tubes if the coldest temperature is greater thanabout 375° C. Similarly, the occurrence of the red polycrystallinematerial could be greatly reduced by keeping the lowest temperatures ator above 450° C.

We have also found that polycrystalline MP₁₅ will not form in singlesource apparatus. The polycrystalline and amorphous materials formed areall high x materials where x is much greater than 15.

METHOD 2. The woven tape holders serve not only to orient the reactiontube but also as effective barriers to heat-transfer between the threeheating zones. These barriers give rise to steeper drops between thezones, but a flatter gradient within the center zone. The result is astep-like temperature profile, which can be manipulated to selectivelyproduce products by providing appropriate ranges of depositiontemperatures.

A. Determination of Product Deposition Temperatures

In von Schnering's announcement of the preparation of single crystals(whiskers) of KP₁₅, he described the preparation from the elements asentailing the heating of the elements--potassium and red phosphorus--ina "temperature gradient" of "600/200° C.", in a 20 cm or so quartz tube.He further states the crystals form at "300° to 320° C.". The furnacesused were apparently single element furnaces in which the gradientarises via heat loss from one end of the tubes sticking out of thefurnace.

In the first improvement on this procedure, a threezone furnace as shownin FIG. 3, with independently controlled heating elements, and a 61 cmlong heating chamber (Lindberg Model 54357 3-zone furnace) was employed,to achieve and control the applied gradient. By supporting the reactiontube, which was now extended to approximately 52 cm long, in a second,open quartz tube, which was, in turn, supported by asbestos blocks, agenerally linear temperature gradient, ΔT/d, was approximately constantbetween the centers of the two outside heating elements. The power tothese elements were controlled by a Lindberg Model 59744-A ControlConsole, which uses three, independent SCR-proportional band controllersto maintain the temperatures selected on manually set thumb-wheels.

The linearly-falling gradient, applied over the long dimensions of thereaction tube, served to cleanly separate the variety of productmaterials formed in the reaction. The products occur in a characteristicpattern of decreasing temperature of deposition: dark purple to blackpolycrystalline films; a ring of massed crystallites; single crystals or"whiskers"; red films of small-grain, polycrystalline morphology, and,at the coldest temperatures, dark grey, amorphous materials.

Example I

A Lindberg Model 54357 3-zone furnace as shown in FIG. 3 comprisingheating elements embedded in a refractory material in separatecylindrical sections of 15.3 cm, 30.6 cm and 15.3 cm lengths, for atotal heating chamber length of 61 cm was used for this example. Thediameter of the chamber is 8 cm. Controlling thermocouples (not shown)are located at about 7.0, 30.5, and 53.5 cm along the 61 cm length.

The ends of the heating chamber were plugged with glass wool to minimizeheat loss from the furnace. A 60 cm long by 4.5 cm diameter quartz tubewas held at a slight angle, by asbestos blocks, in the heating chamber.

The quartz reaction tube was round bottomed, 49 cm long by 2.5 cm indiameter, and reduced to a narrow addition tube 10 cm long by 1.0 cmwide. Under a dry nitrogen atmosphere, 6.51 g of red phosphorus and 0.62g of potassium were transferred into the tube. The atom to atom ratio ofphosphorus to metal was 13.3 to 1. The phosphorus was reagent grade (J.T. Baker). The tube was evacuated to 10⁻⁴ Torr and sealed by fusing theaddition tube several cm's from the wider part of the tube such that thetotal length was 51.5 cm. The sealed tube was placed in the 3-zonefurnace as described above and the set point temperatures of the threezones brought to 650° C., 450° C., and 300° C. over a period of 5 hours,and held there for another 164 hours. The power was shut off and theoven allowed to cool to ambient temperatures at the inherent coolingrate of the furnace. The tube was cut opcn under a dry nitrogenatmosphere in a glove bag. The products consisted of crystalline,polycrystalline, and amorphous forms.

In Table III, the different processing parameters used for several otherruns are listed, along with the types of products observed in each run.Prior to being cut open, the tubes from the first three runs wereinspected as to the positions along the tubes of several products: thedark ring of massed crystallites, and the start of red polycrystallinefilms. The whiskers were always observed between these two points. Thesepositions were later correlated to the temperatures along the gradientscreated by the noted set points. These data are recorded in Table IV.

                                      TABLE III                                   __________________________________________________________________________       P/M                        Time  Tube                                      Ref.                                                                             Charge                                                                            M    P   Press.                                                                             T.sub.1                                                                          T.sub.2                                                                          T.sub.3                                                                          Hours Length                                    No.*                                                                             Ratio.sup.a                                                                       grams                                                                              grams                                                                             Torr..sup.b                                                                        °C.                                                                       °C.                                                                       °C.                                                                       VT/Total.sup.c                                                                      cm  Products.sup.d                                                                       Remarks                        __________________________________________________________________________    1  13.3                                                                              0.21(K)                                                                            6.51                                                                              1 × 10.sup.-4                                                                650                                                                              450                                                                              300                                                                              164/172                                                                             51.5                                                                              S.C., P.C., a                                                                        Example I                      2  12.5                                                                              0.67(K)                                                                            6.56                                                                              1 × 10.sup.-3                                                                600                                                                              465                                                                              350                                                                              138/147                                                                             52.0                                                                              S.C., P.C., a                         3  15.1                                                                              0.67(K)                                                                            8.02                                                                              5 × 10.sup.-4                                                                550                                                                              475                                                                              400                                                                              236/245                                                                             52.0                                                                              S.C., P.C.                                                                           Tube                                                               approx     failed                         4  15.0                                                                              0.29(Na)                                                                           5.86                                                                              7 × 10.sup.-5                                                                600                                                                              450                                                                              375                                                                              72        S.C., P.C., a                         5  30.0                                                                              0.15(Na)                                                                           6.00                                                                              1 × 10.sup.-5                                                                600                                                                              460                                                                              350                                                                              100.5     S.C., P.C., a                                0.55(Rb)                                                               __________________________________________________________________________     .sup.a Atom to atom                                                           .sup.b Pressure at seal off, in Torr                                          .sup.c Where one time is shown, it is the time at the noted gradient          Where two times are shown the second is the total residence time in the       furnace                                                                       .sup.d S.C. = single crystal (or whisker, as often referred to)               P.C. = Polycrystalline material, normally thick films (greater than 10        microns)                                                                      a = Amorphous material                                                        *The same reference numbers are used to refer to the same runs throughout     the tables                                                               

                                      TABLE IV                                    __________________________________________________________________________    Position of High × Products as a Function of Set Temperatures in        3-Zone furnace                                                                                                            Zone                                                                     Deposit                                                                            Temp.                             Ref.                                   Length                                                                             Range                             No.                                                                              Profile                                                                           T.sub.1                                                                          T.sub.2                                                                          T.sub.3                                                                          Time Ring Temp.                                                                             Films                                                                              Temp.                                                                             cm   T                                 __________________________________________________________________________    1  1   650                                                                              450                                                                              300                                                                              7 days                                                                             26.0 cm                                                                            475° C.                                                                    30.0 cm                                                                            435° C.                                                                      4 cm                                                                             40° C.                     2  2   600                                                                              465                                                                              350                                                                              5 days                                                                             26.5 cm                                                                            485° C.                                                                    33.0 cm                                                                            450° C.                                                                     6.5 cm                                                                            35° C.                     3  3   550                                                                              475                                                                              400                                                                              10 days                                                                            23.5 cm                                                                            505° C.                                                                    36.5 cm                                                                            460° C.                                                                    13.0 cm                                                                            45° C.                     3  4   610                                                                              485                                                                              400                                                                              3 days                                                                             26.0 cm                                                                            510° C.                                                                    34.5 cm                                                                            455° C.                                                                    13.5 cm                                                                            55° C.                     3  5   615                                                                              485                                                                              400                                                                              3 days                                                                             28.5 cm                                                                            495°   C.                                                                  42.0 cm                                                                            450° C.                                                                    13.5 cm                                                                            45° C.                     __________________________________________________________________________     Profiles 1, 2 and 3 were all used independently on separate samples to        produce products. Profiles 4, and 5 are reheating profiles used on the        reaction run Ref. No. 3 orginally using profile 3                             Whiskers were found growing in all samples in the space between the ring      and the deposited films.                                                      Temperature readings are estimated accurate to ±5° C.               Position readings are estimated accurate to ±0.5 cm.                  

The information from these two tables was used to establish therelationship of temperature and product-type. The single crystals ofKP₁₅ appear to form over a temperature range of about 40°±10° C., thecenter of which varies from run to run, but which lies around 465°-475°C. Similarly, the onset of deposition of red, polycrystalline materialsappears to be about 450°±10° C. Finally amorphous material depositedeven when the lowest temperature was around 350° C. When this was raisedto 400° C., no amorphous material was observed. (Although the run inwhich this temperature was used eventually ended in a failure of thereaction tube, before products could actually be harvested thistemperature-product relationship for the amorphous material wasconfirmed in later runs using more advanced techniques). Assuming amid-range value, an upper limit for deposition of amorphous material wastaken as about 375° C. The pressures in the heated tubes were notmeasured.

B. Temperature Gradients Which Favor Growth of Single Crystals(Whiskers)

Using the knowledge of the deposition temperature-product morphologyrelationships of Tables III and IV, improvements in the synthetictechnique were sought which would allow greater selectivity of producttype. Methods were sought for manipulating the temperature profiles inthe furnaces which would result in larger areas of the tube surfacebeing within the appropriate temperature ranges for given products.Several available materials with low thermal conductivities, and ineasily manipulatable forms were checked for use as barriers to heattransfer in the furnaces. Woven tapes of asbestos proved a suitableproduct for both supporting the reaction tubes and creating complexgradients, consisting of areas of fairly flat, or isothermal,temperatures, separated by areas (across the barriers) of steep drops orgradients. These so-called "step-like" profiles were applied in all thesubsequent examples where specific products were being sought in maximumyields.

Another improvement which helped gain more reproducible temperaturuprofilcs from run to run was to use a more solid, ceramic type ofmaterial to fill the gaps in the heating chamber walls. In early runs,these were plugged with glass wool, which helped stem loss of heat, butnot very efficiently. The large cylindrical gaps are present in thechamber walls because the furnaces are actually designed to hold aprocess tube along its length, for flow-through applications, ratherthan for enclosed systems, as are being run in these methodologies.

The following examples were all aimed at trying to promote growth ofsingle crystals, both larger in size, and in greater yields, both as apercentage of product forms, and in absolute yields. These results wereindeed achieved.

Example II

A Lindberg Model 54357 3-zone furnace identical in design and size asthat of Example I was also used in this example. The elements werelikewise driven by the same manually set model 59744-A Control Console.The ends of the heating chamber were plugged with a heat resistantceramiclike material, to minimize heat loss from the furnace. Thereaction tube was supported in the heating chamber by two rings of woventape of asbestos. One of these was located between 16-19 cm and theother between 42 and 45 cm along the chamber. This put both ringscompletely inside the center heating section, just beside the junctionsof the center elements and those of the two outer sections. The ringswere constructed such that the tube was held at a slight angle. The ringserved to insulate the heating zones from each other by acting asbarriers to heat transfer.

The quartz reaction tube (FIG. 3) was round bottomed, 48 cm long by 2.5cm in diameter, and reduced to a narrow addition tube 162, 10 cm long by1.0 cm wide. Under a dry nitrogen atmosphere, 5.47 g of red phosphorusand 0.50 g of potassium were transferred into the tube. The atom to atomratio of phosphorus to metal was 15.1. The phosphorus was 99.9999% pure.The potassium was 99.95% pure. The tube was evacuated to 10⁻⁴ Torr andsealed by fusing the addition tube several cm's from the wider part ofthe tube such that the total length was 52 cm. The sealed tube wasplaced in the 3-zone furnace as described above and the set pointtemperatures of the three zones brought to 600° C., 475° C. and 450° C.over a period of 4 hours, and held there for another 76 hours. The powerwas shut off to all three zones at once and the oven allowed to cool toambient temperatures at the inherent cooling rate of the furnace. Thetube was cut open under a dry nitrogen atmosphere in a glove bag. Theproducts consisted of crystalline and polycrystalline forms

Table V lists the processing parameters for a number of other such runs(data for the above example are from the run with reference number 10).

                                      TABLE V                                     __________________________________________________________________________       P/K                              Tube                                      Ref.                                                                             Charge                                                                            Grams                                                                              Grams                                                                             Press.                                                                             T.sub.1                                                                          T.sub.2                                                                          T.sub.3                                                                          Time  Length                                    No.                                                                              Ratio.sup.a                                                                       K    P   Torr.sup.c                                                                         °C.                                                                       °C.                                                                       °C.                                                                       VT/Total.sup.d                                                                      cm                                        __________________________________________________________________________     6 15.1                                                                              0.58 6.80                                                                              7 × 10.sup.-4                                                                600                                                                              485                                                                              450                                                                              24/28 50                                         7 4.93                                                                              1.54 6.01                                                                              1 × 10.sup.-3                                                                600                                                                              485                                                                              450                                                                               96/106                                                                             about 48                                   8 4.98                                                                              1.53 6.03                                                                              7 × 10.sup.-4                                                                600                                                                              475                                                                              450                                                                               96/106                                                                             about 49                                   9 15.1                                                                              0.50.sup.b                                                                         .sup. 5.98.sup.b                                                                  1 × 10.sup.-4                                                                600                                                                              475                                                                              450                                                                              144/  52.5                                      10 15.1                                                                              0.50.sup.b                                                                         .sup. 5.97.sup.b                                                                  1 × 10.sup.-4                                                                600                                                                              475                                                                              450                                                                              144/  52.0                                      11 30.3                                                                              0.25 6.00                                                                              5 × 10.sup.-4                                                                600                                                                              470                                                                              450                                                                              72/78 51.0                                      12 29.7                                                                              0.27 6.36                                                                              1 × 10.sup.-5                                                                600                                                                              470                                                                              450                                                                              72/78 51.0                                      13 14.3                                                                              0.18(Rb)                                                                           5.70                                                                              1 × 10.sup.-5                                                                550                                                                              475                                                                              400                                                                              about 50.0                                                                    144/                                            14 15  0.30(Na)                                                                           6.12                                                                              7 × 10.sup.-5                                                                600                                                                              450                                                                              375                                                                               72/  about 50                                  15 7   0.19(Li)                                                                           5.87                                                                              7 × 10.sup.-5                                                                600                                                                              450                                                                              450                                                                               72/184                                                                             about 50                                  __________________________________________________________________________     .sup.a atom to atom                                                           .sup.b high purity materials K, 99.95% P, 99.9999%                            .sup.c pressure at sealoff Torr                                               .sup.d time at gradient/total resident time in hours                     

All of thcse runs resulted in crystalline and polycrystalline forms. Theyields of the single crystals were always greater than in Example I. Thepolycrystalline materials were always in the form of films deposited inthe colder ends of the tubes and were usually limited to the last 10 orso cm of the tube, though there was usually some overlap with the singlecrystals. Single crystals from these runs were characterized by X-raypowder diffraction patterns as having the same structure as KP₁₅ asdetermined from XRD data. Wet chemical analysis of the crystals weredifficult to obtain with great accuracy, in part because of theirstability, which required extreme conditions for digesting the materialsfor analysis. (See the tables VIII through XI on analytical data below)

The polycrystalline films were also characterized b X-ray powderdiffraction methods and wet methods. The films showed varying degrees ofcrystallinity, and the patterns were similar in several aspects to thatof KP₁₅, but yet were distinctly different in others. Furthermore, thewet analysis, coupled with flame emission spectroscopy consistentlyshowed the alkali metal content to be in the part per million range(i.e. less than 1000 ppm and often less than 500 ppm), and with P/Kratios ranging from about 200 to 1 to about 5000 to 1.

C. Thermal Gradients Which Favor Growth of Polycrystalline and AmorphousMaterials

Following the successful improvements in production of single crystalmaterials, a similar series of experiments were carried out tomanipulate the 3-zone furnace and asbestos rings to find the steppedthermal gradients appropriate to selectively produce the polycrystallineand amorphous materials observed in earlier runs.

These earlier runs suggested the temperatures necessary for obtainingthe desired products. What remained to be shown was how to optimizethese products Table VI shows the type of profiles used and the productsobserved.

                                      TABLE VI                                    __________________________________________________________________________       P/K                             Tube                                       Ref.                                                                             Charge                                                                             K   P   Press.                                                                             T.sub.1                                                                          T.sub.2                                                                          T.sub.3                                                                          Time Length                                                                             Products Observed.sup.f               No.                                                                              Ratio.sup.a                                                                        grams                                                                             grams                                                                             Torr.sup.d                                                                         °C.                                                                       °C.                                                                       °C.                                                                       Hours.sup.e                                                                        cm   W  P a                                __________________________________________________________________________    16 .sup. K/P.sub.15.sup.b                                                             0.50.sup.b                                                                        5.63.sup.b                                                                        3 × 10.sup.-4                                                                600                                                                              465                                                                              350                                                                              72/96                                                                              51.0  X*                                                                              X X                                17 K/P.sub.5                                                                          1.43                                                                              5.66                                                                              5 × 10.sup.-4                                                                600                                                                              425                                                                              400                                                                              72/96                                                                              50.5 X  X none                              4 K/P.sub.5                                                                          1.49                                                                              5.40                                                                              7 × 10.sup.-4                                                                600                                                                              375                                                                              350                                                                              72   about                                                                              X  X questionable                                                        50                                         18 K/P.sub.5                                                                          1.52                                                                              6.00                                                                              1 × 10.sup.-5                                                                600                                                                              350                                                                              350                                                                              99.5 24.0 X  X questionable                     19 K/P.sub.5                                                                          1.25                                                                              4.95                                                                              5 × 10.sup.-4                                                                600                                                                              225                                                                              225                                                                              50/77                                                                              37.0 X  X small amount                                                                  thin film                        20 .sup. K/P.sub.15.sup.b                                                             (6.1-BM).sup.b,c                                                                      5 × 10.sup.-4                                                                600                                                                              440                                                                              325                                                                               72/124                                                                            47.0 X  X questionable                     __________________________________________________________________________     .sup.a atom and atom ratio                                                    .sup.b pure starting elements                                                 .sup.c BM  ball milled mixture                                                .sup.d pressure at seal off                                                   .sup.e time at gradient/total time in furnace                                 .sup.f Wwhiskers(single xtal)                                                 Ppolycrystalline films                                                        aamorphous material                                                           *Product observed                                                        

The first run, which is the subject of the Example III just duplicatedthe temperatures of the ranges used in Example I, the linear fallinggradients now changed to a stepped gradient. Not surprisingly, allproduct types were found, with some variation in quantity, compared tothose of section A. When the coldest temperature was raised to 400° C.,as in the second run of Table VI, no amorphous material was found, asanticipated. With the 425° C. centersection temperature, however, nearlytwo-thirds of the tube's interior was covered with polycrystallinefilms, and only a small number of whiskers were found, meaning the filmscould be produced almost exclusively

In the third and fourth runs, though, where the coldest temperatureswere held at 350° C. (cold enough for amorphous material to be formed inthe first run), and the center zone temperatures were lowered to 375°and 350° C., the amorphous materials were not formed in large amounts atall Instead, large amounts of both single crystals and polycrystallinematerial were found over a fairly short space of the tube, and at best,only thin films of amorphous materials may have formed in the rest ofthe tubes The same phenomenon was observed in the next two runs as well,although there were definitely thin amorphous films in one run.Apparently most vapor species are condensed out in the polycrystallineand single crystal forms and no significant vapor travels to the regionwhich is cold enough to form amorphous forms

Example III

A Lindberg Model 54357 3-zone furnace identical in design and size asthat of Example I, was also used in the example. The elements werelikewise driven by the same manually set Lindberg Model 59744-A ControlConsole The ends of the heating chamber were plugged with heat resistantmaterial to minimize heat loss from the furnace. The reaction tube wassupported by two rings of woven asbestos t.ape One of the rings waslocated between 16-19 cm and the other betwcen 42 and 45 cm along thechamber. This puts both rings completely inside the center heating zone,just beside the junctions of the center elements with those of the twoouter sections. The rings were constructed such that the tube was heldat an angle. The rings also served to insulate the heating zones fromeach other, by acting as barriers to heat transfer.

The quartz reaction tube was round bottomed, 48 cm long by 2.5 cm indiameter, and reduced to a narrow addition tube 10 cm long by 1.0 cmwide. Under a dry nitrogen atmosphere, 5.93 g of red phosphorus and 0.50g of potassium were transferred into the tube. The atom ratio ofphosphorus to metal was 15. The phosphorus was 99.9999% pure. Thepotassium was 99.95% pure. The tube was evacuated to 3×10⁻⁴ Torr andsealed by fusing the addition tube several cm's from the wider part ofthe tube such that the total length was 51 cm. The sealed tube wasplaced in the 3-zone furnace as described above. The temperaturegradient was driven to 600° C., 465° C. and 350° C. over a period ofhours and held there for 72 hours. The power to the elements was thenshut off simultaneously and the furnace allowed to cool to ambienttemperatures at the inherent cooling rate of the furnace. The tube wascut open under a dry nitrogen atmosphere in a glove bag. The productsconsisted of single crystals, polycrystalline films and amorphousmaterial.

D. Production of Cylindrical Boules of Amorphous Polyphosphides

It was evident from the experiments described in section C that toobtain large amounts of amorphous material improvements needed to bemade in the processes alread being used. It was recognized that in orderto get bulk forms of the material, as opposed to thin films, theconditions appropriate for growth had to be confined to a smaller spacethan previously allowed. This translated into allowing only the extremeend of the tube to be at or below 375° C. or so. This was accomplishablein principle by use of the thermal barriers. However, it was alsorecognzied that if the conditions for formation of other materials, i.e.single crystalline MP₁₅ or polycrystalline MP_(x) (x is much greatcrthan 15), were also available over a large area of the tube, thesematerials would act as "traps" for vapor species. It was therefore, alsonecessary to discourage the formation of the other materials. This wasaccomplished by raising the center zone temperatures to levels whichwould be too high for formation of polycrystalline or single crystals.The only area then where these materials were favored were through thearea of the thermal barrier, where rapid temperature drops occurred.

As shown by the following example, and other experiments summarized inTable VII below, further improvements in the procedure were worked out.The first was the use of Honeywell Model DCP7000 Digital ControlProgrammers to drive the heating elements. This allowed thepre-programming of the temperature changes such that reproducibletreatments could be made from run to run. Both controlled heat-ups andcool-downs could be accomplished, eliminating tube failures, andproduction of white phosphorus. The latter often occurred when tubeswere cooled rapidly and phosphorus vapor condensed as P₄. This was oftenthe reason materials appeared reactive. This reactivity could often beremoved by soaking the materials in solvents which would dissolve awaythe white phosphorus. The second improvement was the routine of applyingan "inverted gradient" of 300°-490°-500° C. across the tube from themetal/phosphorus source to the deposition zones before vapor transport,which cleared the deposition zones of materials, which might affectnucleation processes.

By far, the most important improvement, however, was redesigning thegeometry of the tube. Instead of a long tube of nearly uniform 2.5 cmdiameter, the body of the tube was shortened to about 30-32 cm and the10 mm diameter addition tube 160 (FIG. 2) lengthened and sealed suchthat about 5-7 cm of this tube remained as available space in theinterior of the tube. When this latter section was placed in zone 3, andthe vapor transport gradient applied, this section became filled withsolid, bulky cylinders of increasing length, as the conditions forgrowth were improved.

Example IV

A Lindberg Model 54357 3-zone furnace, identical in design and size asthat of Example I was also used in this example. The elements, however,were driven by a Honeywell Model DCP-7700 Digital Control Programmerwhich enabled processing to be pre-programmed and carried out in areproducible fashion.

The ends of thehheating chamber were plugged with heat resistantmaterial to minimize heat loss from the furnace. The reaction tube wassupported by two rings of asbestos tape. The rings were constructed suchthat the tube was held at a slight angle. The rings also served toinsulate the heating zones from each other.

The quartz reaction tube was round bottomed, 33 cm long by 2.5 cm indiameter, and reduced to a narrow addition tube 162, 20 cm long by 1.0cm wide. Under a dry nitrogen atmosphere, 7.92 g of a ball milled chargeof atom to atom ratio of 15 to 1 was loaded into the tube which wasevacuated to 1 ×10⁻⁴ Torr and sealed by fusing the addition tube 10 cmfrom the wider part such that the total length was 43 cm long. Thesealed tube was placed in the 3-zone furnace using the woven barriersdescribed above.

With the tube between 6 and 49 cm, one thermal barrier at 16-19 cm andthe other at about 38-40 cm, the Honeywell Programmer was used to applyan "inverted gradient" of 300°, 490°, 500° C. for 10 hours. After thefurnace cooled at the inherent rate of the furnace, the tube was movedto lie between 12 and 55 cm. The thermal barriers were also rearrangedto lie at 18.5-21.0 cm and 44.5-47 cm. The programmer then drove thegradient to 600°, 485°, 300° C. for 64 hours. The programmer then tookthe tube through a controlled cool-down sequence to a 180°, 190°, 200°C. gradient, which was held for 4 hours. The furnace was then allowed tocool to ambient temperatures at the inherent cooling rate of thefurnace.

The tube was cut open under a dry nitrogen atmosphere and 4.13 grams ofa 2-3 cm long solid homogeneous amorphous boule recovered from theaddition tube 160 (FIG. 3).

The results of several other runs are shown in Table VII.

                                      TABLE VII                                   __________________________________________________________________________               Wt. Press.*                                                                            T.sub.1                                                                          T.sub.2                                                                          T.sub.3                                                                            Time Tube  Yield                               Ref. No.                                                                           Charge                                                                              grams                                                                             Torr °C.                                                                       °C.                                                                       °C.                                                                         Hours                                                                              Length cm                                                                           Amorphous.sup.1                     __________________________________________________________________________    20   K/P.sub.15 BM                                                                       6.1 5 × 10.sup.-4                                                                600                                                                              440                                                                              325   72/124                                                                            47.0  not                                                                           determined                          21   K/P.sub.15 BM                                                                       6.05                                                                              6 × 10.sup.-4                                                                600                                                                              460                                                                              300  64/78                                                                              39.0  1.5 cm boule                        22   K/P.sub.15 BM                                                                       5.72                                                                              1 × 10.sup.-5                                                                600                                                                              475                                                                              300/200                                                                            64/78                                                                              38.0  1.5 cm boule                        23   K/P.sub.15 BM                                                                       5.87                                                                              1 × 10.sup.-5                                                                600                                                                              485                                                                              300/200                                                                            64.78                                                                              40.0  4.0 cm boule                        24   K/P.sub.15 BM                                                                       8.05                                                                              5 × 10.sup.-5                                                                600                                                                              485                                                                              300   64  47.0  58%                                 25   K/P.sub.7 BM                                                                        7.39                                                                              5 × 10.sup.-4                                                                600                                                                              485                                                                              300   64  44.0  36%                                 26   K/P.sub.15 BM                                                                       7.92                                                                              1 × 10.sup.-4                                                                600                                                                              485                                                                              300   64  43.0  52%                                 27   K/P.sub.5 BM                                                                        7.83                                                                              5 ×  10.sup.-5                                                               600                                                                              485                                                                              300  104  41.0  12%                                 28   K/P.sub.15 BM                                                                       8.0 1 × 10.sup.-4                                                                600                                                                              500                                                                              300  104  43.5  53%                                 29   K/P.sub.15 BM.sup.b                                                                 7.95                                                                              1 × 10.sup.-5                                                                600                                                                              485                                                                              300  104  45.5  54%                                 30   K/P.sub.35 BM                                                                       7.78                                                                              5 × 10.sup.-4                                                                600                                                                              500                                                                              300  104  35.0  66%                                 31   KP.sub.125 CP                                                                       5.40                                                                              5 × 10.sup.-4                                                                600                                                                              500                                                                              300  104  34.5  71%                                 32   KP.sub.15 CP                                                                        6.96                                                                              1 × 10.sup.-5                                                                600                                                                              500                                                                              300  104  35.0  51%                                 33   Rb/P.sub.15 BM                                                                      7.50                                                                              5 × 10.sup.-5                                                                600                                                                              500                                                                              300  104  45.5  43.0%                               34   RbP.sub.15 CP                                                                       7.19                                                                              1 × 10.sup.-5                                                                600                                                                              500                                                                              300  104  33.5  37.1%                               35   Na/P.sub.15 BM                                                                      8.58                                                                              1 × 10.sup.-5                                                                600                                                                              500                                                                              300  104  34    46.7%                               36   NaP.sub.15 CP                                                                       7.45                                                                              1 × 10.sup.-5                                                                600                                                                              500                                                                              300  104  34.5  53.7%                               37   Cs/P.sub.15 BM                                                                      9.73                                                                              5 × 10.sup.-4                                                                600                                                                              500                                                                              300  104  34.0  15.8%                               __________________________________________________________________________     .sup.1 boule length or % of charge                                            CP  condensed phase product as charge                                         BM  ball milled product as charge                                             *pressure at seal off                                                    

The results showed the yields of material to be fairly independent ofthe charge type--i.e. ball milled, or the pre-reacted condensed phaseproducts However, there was a distinct dcpendency of yield on the P/Mratio. The greater the relative amount of metal in the charge, the lowerthe yield of material. As the amorphous material is essentiallyphosphorus, this reflects a lower vapor pressure of phosphorus over ametal-phosphorus charge the greater the metal content; hence, a slowerrate of growth for identical thermal conditions.

Table VIII contains some analytical results on amorphous boulesprepared. It shows potassium content, as determined by wet methods. Italso shows trace constituents shown to be present by Flame EmissionSpectroscopy.

                                      TABLE VIII                                  __________________________________________________________________________    Trace Constituents of MP.sub.x Amorphous Materials                                      K by AA.sup.2                                                                       Constituents Detected by Emission.sup.3 in ppm                Ref. No.                                                                           Charge.sup.1                                                                       in ppm                                                                              at greater than 1 ppm, Values in ppm                          __________________________________________________________________________    21   K/P.sub.15                                                                         427   Fe:                                                                               .4-4                                                                             K: 20-200 Si: 6-60                                     22   K/P.sub.15                                                                          85   Al:                                                                               4-40                                                                             Fe:                                                                               6-60                                                               Si:                                                                              20-200                                                                            K: Less than 30                                        23   K/P.sub.15                                                                         20-224                                                                              As:                                                                               2-20                                                                             Si:                                                                               1-10                                                               Did not check for K                                           24   K/P.sub.15                                                                          40   Fe:                                                                               .3-3                                                                             Si:                                                                               3-30                                                               Did not check for K                                           25   K/P.sub.7                                                                          285   As:                                                                              20-200                                                                            Si:                                                                               4-40                                                               K: 12-120                                                                            Na:                                                                               3-30                                               26   K/P.sub.15                                                                         161   K: 20-200                                                                            Si:                                                                              20-200                                              __________________________________________________________________________     .sup.1 Ball Milled only                                                       .sup.2 Atomic Absorption, on digested sample                                  .sup.3 Flame emission spectrographic analysis, on undigested sample      

Tables IX, X and XI are of analytical data obtained by wet methods onproduct from vapor transport synthesis.

the PM ratios in the tables are atom ratios unless otherwise noted.

                  TABLE IX                                                        ______________________________________                                        SINGLE CRYSTALS (WHISKERS)                                                    FROM VAPOR TRANSPORT                                                          Ref. No.  Charge        P/M    Total*                                         ______________________________________                                        38        K/P.sub.15    19.1   94.5                                            6        K/P.sub.15    19.1   98.8                                           10        K/P.sub.15    19.1   99.4                                           11        K/P.sub.30    16.4   96.1                                           17        K/P.sub.5     11.3   97.7                                           ______________________________________                                         *Analytical mass balance % M + % P detected                              

                  TABLE X                                                         ______________________________________                                        AMORPHOUS MATERIALS FROM                                                      VAPOR TRANSPORT                                                               Ref. No.  Charge      P/M        Total*                                       ______________________________________                                        39        K/P.sub.15  2500    W    100.3                                      16        K/P.sub.15  1750    W    99.7                                       21        K/P.sub.15  2300    W    92.8                                       22        K/P.sub.15  12200   W    97.0                                       25        K/P.sub.7   3500    W    97.9                                       26        K/P.sub.15  6200    W    97.8                                       23        K/P.sub.15  greater than                                                                             98.2                                                               4500    W                                               24        K/P.sub.15  7000    W    93.3                                       24        K/P.sub.15  25000   W    99.5                                       27        K/P.sub.5   greater than                                                                             99.7                                                               84000   E                                               28        K/P.sub.15  7800    W    98.2                                                             82500   E                                               29        K/P.sub.15  25000   E    94.8                                       ______________________________________                                         W Wet analysis                                                                E Flame emission spectroscopy                                                 *Analytical mass balance % M + % P detected                              

                                      TABLE XI                                    __________________________________________________________________________    ANALYSIS OF VAPOR TRANSPORT PRODUCTS                                          __________________________________________________________________________                    HT Films                                                               Residue                                                                              Ring*   Whiskers                                                                             Poly/Films  Poly/Films Amorphous               Ref. No.                                                                           Charge                                                                            Total                                                                             P/M                                                                              Total                                                                             P/M Total                                                                             P/M                                                                              Total                                                                              P/M    Total                                                                             P/M    Total                                                                             P/M                 __________________________________________________________________________    39   K/P.sub.15                                       100.3                                                                             2500                38   K/P.sub.15         94.54                                                                             19.09                                                                            98.40                                                                              1170                                       2   K/P.sub.125                                                                              95.4                                                                              10.4                                                       6   K/P.sub.15         98.76                                                                             19.10                                             10   K/P.sub.15         99.40                                                                             19.07                                              9   K/P.sub.30                                                                        92.35                                                                             4.90                                                                             89.56                                                                             12.04                                                                             96.14                                                                             16.35                                                                            100.4                                                                              infinity                                                                             95.69                                                                             infinity                                                                             96.88                                                                             infinity            17   K/P.sub.5  97.65                                                                             13.1                                                                              100.50                                                                            11.3                                                                             99.51                                                                               213   99.71                                                                              358                                                          99.81                                                                               347   98.97                                                                              193                           16   K/P.sub.15                99.91                                                                              2300   98.20                                                                                54.5                                                                              99.71                                                                             1750                18   K/P.sub.5                 97.91                                                                                  137.65                                40   K/P.sub.30                100.00                                                                             greater than                                                                         100 1800                                                               7000                                      19   K/P.sub.5                                                                         95.00                                                                             2.88                                                             20   K/P.sub.15                                                                        95.4                                                                              3.17                                                                             94.91                                                                             13.3       97.9 1250   98.97                                                                             6250                           21   K/P.sub.15                                                                        80.0                                                                              3.67              98.2 greater than                                                                         99  greater than                                                                         92.8                                                                              2300                                                    2500       2500                           22   K/P.sub.15                                                                        89  3.23                                                                             88.7                                                                              10.92      95.3 2190   93.1                                                                              2900   97.0                                                                              12200               25   K/P.sub.7                                                                         91.2                                                                              3.17              96.3 2000              97.9                                                                              3500                26   K/P.sub.15                                                                        89.7                                                                              3.01                                                                             76.70                                                                             11.5       95.1 4000              97.8                                                                              6200                23   K/P.sub.15                                                                        91.8                                                                              2.80              95.40                                                                              2200              98.2                                                                              4500                __________________________________________________________________________     Total = total percent of metal and phosphorus measured                   

                    KP.sub.x                                                      Ref.     Residue                                                                              Whiskers                                                                             Poly/Films Poly/Films Amorphous                        No.                                                                              Charge                                                                              Total                                                                             P/M                                                                              Total                                                                             P/M                                                                              Total                                                                             P/M    Total                                                                             P/M    Total                                                                             P/M    Remarks               __________________________________________________________________________    24 K/P.sub.15                     93.3                                                                              7000   99.5                                                                              25000                        27 K/P.sub.5                                                                           96.0                                                                              3.28      93.2                                                                              greater than      99.7                                                                              greater                                                                              Ehan                                              9803.sup.E           84,000                       28 K/P.sub.15                                                                          87.7                                                                              3.42      99.5                                                                              greater than      98.2                                                                              greater                                                                              E is                                             12500.sup.E           7800   greater than                                                                  82500                 29 K/P.sub.15                                                                          93.6                                                                              3.48   1250                                                                             98.3                                                                              15000             94.8       E is                     pure                                                 greater than                                                                  25000                 41 Na/P.sub.15         94.13                                                                             greater than                                                                         97.31                                                                             greater than                                                                         98.21                                                                             greater                                                                              Na not                                            700       700        700    detected                                     98.80                                                                             greater than                                                                         97.23                                                                             greater than      Na not                                                      700        700    detected              42 Na/P.sub.15         98.71                                                                             greater than                                                                         97.12                                                                             greater than                                                                         98.47                                                                             greater                                                                              Na not                                            700       700        700    dectected             43 Na/Rb/P.sub.30      97.6                                                                              1000   97.3                                                                              1330                                                           Na/Rb                                                                             4.3/1  Na/Rb                                                                             3.1/1                                   44 Rb/P.sub.14         99  1300                                               45 Li/P.sub.7          96.86                                                                             1500                                               __________________________________________________________________________     Wet analysis unless noted                                                     .sup.E Metal content measured by flame emission spectroscopy in atomic        ratio                                                                         *High temperature (HT) films and rings, see FIG. 2                       

Preparation of Metal Polyphosphides by Two Source Techniques

Polyphosphides have been prepared in two fundamentally different typesof equipment which are both identified herein as Two Source or separatedsource techniques because in both types of equipment, the metal andphosphorus are separated and heated independently on either side of adeposition zone. All examples have been carried out on the K-P system.

In the first method, as shown in FIG. 11, the phosphorus and potassiumcharges are held at opposite ends of a sealed quartz tube 100. The tubeis subjected to a temperature profile as shown in FIG. 12 achieved byuse of a three zone furnace. The profile takes the independent chargesto elevated temperatures, relative to the center zone between the twoconstituents. In this zone, the vaporized constituents combine to formthe deposited product of KP₁₅, in the form of films on the reactorwalls. (More complete details appear in Example V below)

In the second apparatus, as illustrated in FIG. 14, a substantialsection generally indicated at 102 is held outside the three zonefurnace 104, at ambient temperature. This section includes a stopcock106 and ball-joint 108 arrangement used to achieve the low-pressuresdesired to carryout the reaction. This alternate sealing techniquerequires lower temperatures for this portion of the set up, but allowsfor rapid and nondestructive insertion of a glass "boat" which holds thephosphorus and metal sources. The boat 112 (see FIG. 15) also isdesigned to hold metal on glass substrates 114 (FIG. 14) upon which thefilms are to be deposited. These film/substrate configurations serve asinitial starting points for device designs, as indicated below.

The section outside the furnace provides a cold trap for vapor species.Specifically phosphorus, which is loaded into the zone closest to theoutside section, is deposited in the outside section in large amounts,generally as the highly pyrophoric white form. Because this trap exists,the vapor pressure conditions of the system are quite different from thetotally-heated systems described above. It follows that the temperatureconditions which successfully yields desired products in the firstapparatus, are.not appropriate for the second apparatus. The conditionsappropriate for the latter were independently determined.

Example V

In the 54 cm long by 2.5 cm diameter quartz tube 100, with a 10 cm longby 1.0 cm diameter neck 116, shown in FIG. 11, phosphorus and potassiumwere loaded, under dry nitrogen conditions, into opposite ends of thetubes, in a atom to atom ratio of 15 to 1. The potassium (99.95% purewas loaded first by dropping small pieces, totaling 0.28 g weight, intoa cup 118 with the tube oriented vertically. The pieces were then meltedand allowed to resolidify in the cup. The phosphorus (99.9999%) was thenadded to the tube, the 3.33 grams of pieces easily being manipulatedaround the cup 118. The tube was then sealed by fussion of the neck 116,at 5×10⁻⁵ Torr.

The tube was then arranged in a Lindberg Model 54357-S 3-zone furnace tolie centered amongst the three zones. Unlike the Model 54357, which haszone lengths of 6, 12 and 6 inches (15.2, 30.5, and 15.2 cm), the Smodel has zones of 8, 8 and 8 inches (20.3, 20.3, and 20.3 cm). Twowoven asbestos tapes, spiraled around the tube, held it at the junctionsof zones 1 and 2, and zones 2 and 3 Not only did these tapes support thetube, they insulated the center zone from the higher temperatures of theoutside zones. A schematic representation of the resultant temperatureprofile is shown in FIG. 12. A Honeywell Model DCP-7700 Digital ControlProgrammer was used to drive the three ing zones through an appropriatewarm-up period, to the 450°, 300°, 450° gradient, which. was held for 72hours, and then through a 15 hour cool down sequence to ambienttemperature.

The materials formed in the tube were analyzed by the followingprocedure. First, in a dry nitrogen atmosphere, the tube was cut intoseven tubular sections, of approximately equal lengths, by use of asilicon carbide saw. Pieces of the films found in the sections(generally 10 microns or geater in thickness), were removed andindividually examined by X-ray diffraction techniques. The remainder ofeach section was subjected to analysis by wet methods.

The P/K ratios of the deposits found for the sections are indicated inFIG. 13. For the center regions, where T was approximately 300° C., thebulk compositions were about 14/1, which falls within the accuracylimits of the methods employed to identify the material as KP₁₅. Morerevealing were the X-ray powder diffraction patterns for the materialsfound having a P/K of about 14 which clearly showed they matched thoseof KP₁₅, either from single whiskers or bulk polycrystalline material.Furthermore, the patterns clearly showed the presence of bothpolycrystalline and amorphous materials in about a one to one ratio, asmanifested by broadening of the peaks.

Example VI

The apparatus used in this example was modified relative to that ofExample V. The quartz tube 119 was fabricated with "nozzles" 120 and 122segregating the two end chambers from the center one (see FIG. 16).Under dry nitrogen conditions, melted potassium (0.47 g, 99.95% purity)was added to the outside chamber indicated at K, and allowed toresolidify. The addition tube 124 was then fused shut. Phosphorus (5.58g, 99.9999% purity) was then added to the other outside chamberindicated at P and the whole apparatus evacuated and sealed at 1×10⁵Torr, by fusion of the second addition tube 126. The phosphorus topotassium ratio in the system was 15 atoms to 1 atom.

The sealed tube 119 was 41 cm long, and was centered amongst the threeconsecutive 20.3 cm zones of a Lindberg Model 54357-S 3-zone furnace.Two thermal barriers (TB) of woven asbestos tapes, spiraled around thetube, held it at the junctions of zones 1 and 2, and zones 2 and 3. Inaddition to holding the tubes, they insulated the center zone from thehigher temperatures of the outside zones. A Honeywell Model DCP-7700Digital Control Programmer was used to drive the three heating zonesthrough a warm up period, to a 500°, 355°, 700° C. gradient. (Thephosphorus was at 500° C., the potassium at 700° C. The center zonetemperature was selected as 300° C., but because the insulatingcharacteristics of the woven tape is limited, heat spillover from theside chambers raised the center zone temperature to the 355° C. level.)This gradient was held for 80 hours, and then a 24 hour cool-downsequence was followed.

When tube 119 was cut open, under dry nitrogen conditions, using asilicon carbide saw, it was found that nozzle 122 between the potassiumzone K and the center zone had become clogged with material, whichlooked like polyfibrous KP₁₅. The center zone contained thin, light redfilms; thicker, darker red films; and several, relatively large,monolithic boules. The two largest pieces were each about 4 cm long, by1 cm wide, with a maximum thickness of about 4 mm. One side of eachpiece is relatively planer, while the other has a convex configuration,associated with growth against the inside walls of the circular reactiontube.

Wet analysis of this material showed the potassium content to beextremely low, as a bulk analysis, at less than 60 parts per million.Electron Spectroscopy for Chemical Analysis (ESCA) indicated that thepotassium content of this material decreased rapidly outwardly of thetube wall on which it was first deposited. At 100 angstroms the ratio ofP--K was about 50. As measured by ESCA the P--K ratio on the finalsurface deposited was in the order of 1000. X-ray diffraction studiesshowed the material to be amorphous.

Example VII

Under dry nitrogen conditions, 0.19 g of melted potassium (99.95%purity) were transferred to one of the outermost sections 128 (5 cmlong) of a pyrex boat 112 (FIG. 15). The metal was allowed toresolidify. Two plain glass substrates 114 (see FIG. 14), each about 7.5cm long by 1 cm wide, were laid end to end, filling the 15.3 cm longcenter section 130. Next, 1.36 grams of phosphorus (99.999% purityobtained from Johnson Matthey) were added to the opposite outsidesection 132 of the boat. The phosphorus is in a mixed-size granular formwhich readily pours out and fills in the bottom of section 132. Pyrexdividers 113 keep the P and K and substrates from sliding in the boat112. The 35 cm long boat 112 was then carefully slid into the 60 cm longby 2.5 cm diameter pyrex reaction chamber 134 of FIG. 14, until section128 with the potassium abutted the round bottom, closed end of thechamber 136. A Buta-N O-ring, size 124 was then clamped into the O-ringjoint 102, and the teflon Stopcock 106 (supplied by ChemVac, Inc)screwed down tightly. On a vacuum line, the stopcock 106 was reopenedand the chamber pumped down to 8×10⁻⁴ Torr. The stopcock was thenre-closed, sealing the reaction chamber.

The reaction chamber is arranged in a Lindberg Model 54357-S 3-zonefurnace. As shown in FIG. 14, two wovenglass tapes 137 and 139, spiraledaround the tube, supported the chamber at the junctions of zones 1 and2, and zones 2 and 3. These tapes forming thermal barriers (TB) were setto just lie completely within the center zone. A third spiraled tape 138was used to support and thermally insulate the point where the apparatusexits the heating chamber of the furnace. A cylindrical plug 140 of aceramic like material was used to stem heat loss out of the furnaceopening at the other end of the chamber.

This arrangement of the apparatus results in section 128 of the boat 112containing the potassium to lie within the third heating zone, section130 containing substrates to lie in the center, or second, heating zoneand section 132 of the boat containing phosphorus to lie in the firstheating zone. It also results in a large segment of the apparatus beingoutside the furnace, at ambient temperature.

A Honeywell Model DCP 7700 Digital Control Programmer was used to drivethe three heating sections through a warm-up period in which thetemperatures were brought to 100°, 50°, 100° C. in the phosphorus zone,the substrate zone, and the potassium zone, respectively. Then, asrapidly as possible (approximately 18 minutes) the gradient was drivento 500°, 300°, 400° C., where it was held for about 8 hours. The furnacewas then allowed to cool at its inherent rate, to a profile of 100°,100°, 100° C., which took about 10 hours. The furnace then was allowedto cool to room temperature.

The tube 134 was removed from the furnace. The section outside thefurnace contained deposits of white, yellow, and yellow-red materials,all of which were probably phosphorus in varying stages ofpolymerization. The phosphorus heating zone was clear of material, whilethe potassium zone contained a variety of materials, ranging in colorfrom tan, to yellow, to orange.

The latter extended slightly into the center zone, which otherwise wascovered through one-half of its length, next to the potassium zone, witha dark film, which transmitted red light when a source lamp was shonethrough it. The remaining half of the zone was clear of material. Theapparatus was opened under dry nitrogen conditions, the pyrex boat 112withdrawn, and the glass substrates, covered with the red film, removedfrom the boat, and placed in a tightly sealed bottle, for lateranalysis. (When the remainder of the materials were exposed to ambientconditions, the phosphorus deposits in the exposed section of tube wouldgenerally burn vigorously, though those closest to the phosphorus sourcedid not exhibit such reactivity. The materials which were in thepotassium-source section of the apparatus were very reactive whenexposed to moisture. They generally burned vigorously apparently by theproduction of hydrogen via reduction of water.)

The technique was repeated several times. Further examples are noted inTable XII.

                                      TABLE XII                                   __________________________________________________________________________    TEMPERATURES                             DEPOSIT                              REF.                                                                              P  CENTER                                                                              K  TIME                                                                              K    P               LENGTH                               No. °C.                                                                       °C.                                                                          °C.                                                                       HRS.                                                                              GRAMS                                                                              GRAMS                                                                              SUBSTRATES cm    FURNACE                        __________________________________________________________________________    46  500                                                                              300   400                                                                              8.0 0.19 1.47 glass      6.5   A                              47  500                                                                              300   400                                                                              8.0 0.19 1.43 glass and  9.0   A                                                            Ni on glass                                     48  500                                                                              300   400                                                                              8.0 0.26 1.62 Ni on glass                                                                              5.0   A                              49  475                                                                              300   375                                                                              8.0 0.27 1.82 glass      1.0   A                              50  500                                                                              300   400                                                                              8.0 0.15 1.66 glass      1.0   B                              51  550                                                                              300   400                                                                              8.0 0.20 1.72 glass      3.0   B                              52  525                                                                              300   400                                                                              8.0 0.21 1.54 glass      6.5   B                              53  525                                                                              300   400                                                                              8.0 0.21 1.56 Ni/Au/Ni   7.0   B                                                            1000Å/700Å /500Å                    54  500                                                                              300   400                                                                              8.0 0.20 1.51 Ni/Au/Ni   8.5   A                                                            1000Å /700Å /1000Å                  __________________________________________________________________________                                  5                                           

There exist limiting conditions for the preparation of the dark filmswhich transmit red light. If the temperatures in the two source zonesare dropped slightly, as in run number 49 of Table XII, the amount ofmaterial formed, as manifested by the length of the deposit, dropsdramatically. Similarly, subtle differences between the performancecharacteristics of two otherwise identical Model 54357S 3-zone furnacesrequire that in the second furnace (B), the temperature of thephosphorus source be raised to higher temperature (see run numbers 50,51 and 52). Raising the phosphorus source temperature to 550° C. gives agood result, raising it to 525° C. gives a better result.

Analysis of materials from runs 46, 47 and 48, by Scanning ElectronMicroscope with electron diffraction analysis (SEM-EDAX) methodologiesrevealed the material to be KP₁₅ films, on the order of 6-7 microns inthickness, and to be of an amorphous character, with no discerniblestructure evident in the micrographs.

Summary of Vapor Transport Conditions

Processing features for controlling product types are: (1) Use of athree zone furnace for more uniform temperature control; (2) Extendedtube length; (3) Use of thermal barriers for temperature gradientcontrol; (4) Use of thermal plugs at ends of oven; and (5) Use ofextended narrow addition tube to obtain cylindrical boules.

Ranges of conditions for one source vapor transport are:

(1) Reaction zone temperatures range from 650°-550° C.; Cold zonedeposition temperatures range from 450°-300° C.

(2) Deposition temperature for single crystals of KP15 were found torange plus and minus 25° C. around a center value of 465°-475° C.

(3) Deposition temperature for polycrystalline films were found to rangefrom about 455° C. down to 375° C.

(4) Deposition temperature for amorphous forms of the new form ofphosphorus range from about 375° C. down to at least 300° C. (No lowertemperatures were investigated to date)

The range of conditions for two source vapor transport are for formingbulk KP₁₅ materials (FIG. 11 apparatus); Phosphorus, temperature at 450°C., Potassium at 450° C., and deposit zone at 300° C.; deposits werethick films of mixed polycrystalline and amorphous KP₁₅ ; for bulkamorphous KP_(x) (x much greater than 15 the new form of phosphorus,FIG. 16 apparatus): Phosphorus at 500° C., Potassium at 700° C. anddeposit zone at 355° C. K source became plugged, deposit was bulkamorphous KP_(x) ; for thin films of amorphous KP₁₅ (FIG. 14 apparatus)Phosphorus at 500° C., Potassium at 400° C., and substrate at 300° C.

For thin films of KP₁₅, the Phosphorus source may be raised to 525° C.and amorphous KP₁₅ is still produced. If the Phosphorus sourcetemperature is dropped to 475° C., the system does not yield KP₁₅. Ifthe Potassium source temperature is dropped to 375° C., the system doesnot yield KP₁₅. The substrate temperatures may be raised to 315° C. andthe system will still yield KP₁₅, but not if they are raised to 325° C.

Preparation of Polycrystalline Metal Polyphosphides in Large Amounts Via"Condensed Phase Synthesis"

Although not formed in a physical state appropriate to the tapping oftheir useful semiconducting properties, alkali metal polyphosphides ofthe type , MP₁₅, MP₇, and MP₁₁, can readily be prepared in gram or morequantities by a technique we call "condensed-phase" synthesis. Beforeusing this technique, the reactants are generally brought in intimatecontact by a ball-milling procedure. Decagram or more quantities of theelements are loaded in ball-mills, under dry nitrogen conditions, in thedesired metal to phosphorus atom to atom ratio, e.g. P/M 15 to 1 forMP₁₅. The sealed mills are then utilized for 40 or more hours to reducethe components to a well-mixed, homogeneous, free-flowing powder. Themills are generally heated during 20 hours or so of the milling, toabout 100° C. This is done to increase the fluidity of metal componentduring the milling.

A portion of the milled mixture, generally 10 grams or more, istransferred to a quartz ampoule, under dry nitrogen conditions. Theampoule ranges in size from 2.5 cm in diameter by 6.5 cm in length, to2.5 cm in diameter by 25 cm in length, depending on the charge size tobe processed. The tube is sealed at reduced pressure (generally lessthan 10⁻⁴ Torr).

The reaction is carried out by subjecting the tube to an ever increasingtemperature, under isothermal conditions, until the applied temperaturereaches 500° or 525° C. By isothermal conditions we mean that the wholemass of material is always as nearly as practicable at the sametemperature to prevent vapor transport from hot to cold portions whichwould result in non-uniform products. The highest soaking temperature isheld for a substantial time during which a powdery polycrystalline orcrystalline product is formed. A typical soaking time is 72 hours. Thelonger the reaction, or soaking time, the more crystalline the product(as manifested by grain size, sharpness of X-ray powder-diffractionlines, etc). The hot tube is also taken through a cooling period (morethan 10 hours) to ambient temperature. Slow cooling is not necessary forthe reaction, but prevents tube breakage due to the different thermalcoefficients of the products and the quartz ampoule.

Both the heat-up and cool down periods have been observed to best bedevised as relatively long (more than 10 hours) with soaking atintermediate temperatures (e.g., 200°, 300°, 400°, 450° C.) for 4-6hours. Failure to follow these slow heat-ups or cool-downs oftenresulted in explosions of the reaction tubes. However, the products ofthe condensed phase reactions were the same as in slow cool down exceptthat a small quantity of residual phosphorus would be white rather thanred phosphorus.

Example VIII

19.5 grams of a ball milled mixture of reagent grade phosphorus andpotassium, in a atom to atom ratio of 15 to 1, was transferred into a6.5 cm long by 2.5 cm diameter quartz tube, which tapered to a 8 cm longby 1.0 cm diameter section. The transfer was carried out under drynitrogen conditions. The tube was sealed at reduced pressure (1×10⁻⁴Torr) by fusing the narrow section a centimeter or so above the widerpart of the tube.

The tube was supported in the center zone of a Lindberg Model 54357three-zone furnace by a second quartz tube, or liner, which was, inturn, supported in the radial center of the heating chamber by asbestosblocks. The 3-zone furnace heating elements were driven by a HoneywellModel DCP-7700 Digital Control Programmer which enables processing to bepreprogrammed and carried out in a reproducible fashion. Using theprogrammer, the reaction tube was subjected to the followingtemperatures for the indicated lengths of time: 100° C., 1 hr; 450° C.,6 hrs.; 500° C., 18 hrs.; 525° C., 72 hrs.; 300° C., 2 hrs.; and 200°C., 4 hrs. (When all three zones are controlled at the same temperature,the center zone is highly isothermal, with a temperature variance ofless than 1° C. across the zone).

After the furnace cooled to ambient temperature, at the inherentcooling-rate of the furnace, the reaction tube was removed from thefurnace. Under dry nitrogen conditions the quartz ampoule was cut openusing a silicon-carbide saw, and the dark purple, polycrystalline massremoved. A sample of the material was subjected to compositionalanalysis. Wet analysis gave a P/K ratio of about 14.2 to 1, which isaccurate to about 6% of the theoretical value of 15 to 1. Products fromsimilar runs on K/P₁₅ charges fell the same range values, as shown inTable XIII.

                                      TABLE XIII                                  __________________________________________________________________________    CONDENSED PHASE PRODUCTS                                                                         TOTAL  CHARGE                                                                              HIGHEST                                                                             TIME AT                                                                             TOTAL                             REF.                                                                              CHARGE  PRODUCT                                                                              PRODUCT                                                                              SIZE  TEMP. HIGH T.                                                                             OVEN   PRESSURE                   NO. RATIO   P/M    %      GRAMS °C.                                                                          HRS.  TIME HRS.                                                                            TORR**                     __________________________________________________________________________    55  K/P.sub.15                                                                            15.3   85.5   5.5   500   120.5 140    1 × 10.sup.-5        56  K/P.sub.15                                                                            15.5   99.0   21.2  525   305.0 320    5 × 10.sup.-4        57  K/P.sub.15                                                                            16.2   97.2   9.2   525   266.0 380    5 × 10.sup.-3        58  K/P.sub.15 (Pure)                                                                     14.0   99.3   8.8   525   216.0 292    5 × 10.sup.-4        59  K/P.sub.15                                                                            14.2   94.0   19.2  525   72.0  120    1 × 10.sup.-4        60  K/P.sub.15                                                                            13.6   96.5   17.7  525   72.0  120    1 × 10.sup.-4        61  K/P.sub.15                                                                            14.7   97.8   16.7  525   72.0  120    6 × 10.sup.-4        62  Rb/P.sub.15                                                                           14.9   99.8   9.4   525   216.0 292    5 × 10.sup.-4        63  Rb/P.sub.15                                                                           12.9    97.05 16.1  525   72.0  120    N.D.                       64  Cs/P.sub.15 (Pure)                                                                    15.5   95.5   13.9  500   120.0 390    5 × 10.sup.-4        65  Cs/P.sub.15 (Pure)                                                                    N.D.   N.D.   15.9  500   260.0 710    1 × 10.sup.-5        66  Na/P.sub.15                                                                           19.2   97.7   9.1   525   216.0 292    5 × 10.sup.-4        67  Na/P.sub.15 (Pure)                                                                    14.9   92.7   13.5  500   260.0 710    1 × 10.sup.-5        68  Li/P.sub.15                                                                            16.35 96.9   7.8   525   144.0 240    1 × 10.sup.-4        69  Rb/P.sub.7 (Pure)                                                                      6.2   96.8   16.3  500   72.0  130    1 × 10.sup.-5        70  Rb/P.sub.7 (Pure)                                                                     N.D.   N.D.   17.2  500   72.0  130    1 × 10.sup.-4        71  Cs/P.sub.7 (Pure)                                                                      7.1   96.2   18.6  500   72.0  130    1 × 10.sup.-5        72  Cs/P.sub.7 (Pure)                                                                     N.D.   N.D.   7.9   500   172.0 290    1 × 10.sup.-4        73  Na/P.sub.7                                                                             6.5   93.6   11.5  500   168.0 360    1 × 10.sup.-5        74  K/P.sub.15                                                                            N.D.   N.D.   14.7  525   72.0  120    5 × 10.sup.-4        75  K/P.sub.15 (Pure)                                                                     N.D.   N.D.   16.1  525   144.0 240    1 × 10.sup.-3        76  K/P.sub.15                                                                            N.D.   N.D.   31.9  500   169.0 330    5 × 10.sup.-4        77  K/P.sub.15                                                                            N.D.   N.D.   28.4  525   144.0 240    5 × 10.sup.-4        78  K/P.sub.15                                                                            N.D.   N.D.   36.4  525   144.0 240    1 × 10.sup.-4        79  K/P.sub.15                                                                            N.D.   N.D.   32.1  525   72.0  124    1 × 10.sup.-5        __________________________________________________________________________     *Example                                                                      N.D. Not Determined                                                           **When tube sealed                                                       

In addition, several samples from different runs were subjected tomorphological analysis. The XRD powder diffraction patterns for thesematerials were readily matched to those obtained from the single crystalKP₁₅ samples produced by the vapor-transport methods cited elsewhere.

The methodology was carried over to other metal-phosphorus systems, asis indicated in the table. Comparisons of the XRD data of thesematerials, both with each other and that obtained on single crystalsestablished the analogous nature of the products, i.e. they all havebasically the same all parallel pentagonal tubes of covalently bondedphosphorus.

Milling Metals with Red Phosphorus Introduction

We have utilized ball milling to prepare homogeneous, intimatelycontacted mixtures of red phosphorus with Group 1a and group 5a metals.

The milled products are relatively air stable and they provideconveniently handled starting materials for the previously describedcondensed phase and single source vapor transport techniques. Theirstability indicates that polyphosphides have formed at least in partduring the milling process.

Summary

The group 1a metals (with the exception of lithium) have proved to ballmill easily with red phosphorus. The facility of milling becomes evenmore pronounced with the lower melting metals, typified by rubidium andcesium. A problem arises when the Group 1a M/P ratio is varied from 1/15down to 1/7. The increased metal content generally results in severeagglomeration of the charge onto the walls of the ball mill.Fortunately, the agglomerated products are easily scraped from the milland crushed through a 12 mesh sieve. Lithium and arsenic are somewhatdifficult to mill using the standard ball milling procedure due to theirhardness and higher melting points.

Reagent Purity

The initial experimental work used reagent grade metals and reagentgrade phosphorus. We now use only high purity metals and electronicgrade (99.999% and 99.9999% pure) red phosphorus obtained from JohnsonMatthey.

Mode of Milling A. Standard Ball Milling (Rotation)

This was originally the method of choice for the alkali M/P systems.However, we have used more intensive grinding processes (cryogenic andvibratory milling) for the other group 5a metals.

The stainless steel ball mills were fabricated "in house" and as shownin FIG. 17 comprise a cylinder 150 with these dimensions--4.5" 0.D.×6"height×.]." wall thickness. The top of the mill is provided with aninner flange 151 to accept a Viton O-ring 152. A stainless steel top 154is held in place by a bar 155 tightened down with a screw 156.

One mill has smooth inside walls. The second mill was constructed withthree baffles welded onto the walls from top to bottom. These act aslifters for the balls and reagents and result in more efficientgrinding.

A total of less than 50-60 g reagent charge is desirable. Initialmilling experiments used 1/4" stainless steel balls; we have sinceachieved better results with a mixture of 1/4" and 1/8" stainless steelballs.

Cryogenic Milling (-196° C.)

This was accomplished using the Spex freezer mill (available from SpexIndustries, Metuchen, N.J.).

Due to equipment limitations, only small quantities (2-3 g) can bemilled in a single operation--however, this can be done quickly atliquid nitrogen temperatures (in a matter of a few minutes). Thus, thistechnique finds applicability in reducing to powder form, the harder andhigher melting metals such as lithium and arsenic. These can then beco-ground with red phosphorus in the rotating ball mill or vibratorymill.

Vibratory Milling The equipment (Vibratom) is available from TEMA, Inc.,Cincinnati, Ohio. This is essentially a ball mill, but instead of usinga rotating motion, circular vibrations are generated--similar to that ofa paint shaker. The dimensions of the mill are 51/4" 0.D.×3.5"height×1/8" wall thickness.

The mill does not contain baffles. We have used this mill for thedifficult to mill elements such as As.

Time of Milling

There has been considerable variation here. Generally, the duration ofhot milling is not less than 40 hrs. nor more than 100 hrs. To someextent, this has been determined by the system being milled. Less timeis required for the lower melting Cs and Rb systems.

Temperature of Milling This has either been at ambient temperature orthe mills have been externally heated to approximately 100° C. with aheat lamp. Ambient temperatures are suitable for low melting pointmetals such as Cs (28.7° C.) and Rb (38.9° C.). External heat lampapplication to 75°-100° C. for 3-4 hours was definitely beneficial forthe Na (97.8° C.) and K (63.7° C.) systems. Heating to 100° C. was of novalue with Li (108.5° C.). We conclude that stable products are theresult of milling melted alkali metal and phosphorus. Ball Milling ofK/P₁₅

Example IX (Reference No. 88, Table XIV)

Under nitrogen in a dry box, an unbaffled stainless steel ball millcontaining 884 g of 1/4" stainless steel balls was charged with 6.14 g(0.157 mole) 99.95% pure K (from United Mineral and Chem. Co.) and 72.95g (2.36 mole) of 99.9999% pure red P (from Johnson Matthey Chemicals).The mill was sealed and rotated on a roll station for a total of 71hours. The mill was heated to approximately 100° C. for 4 hours byplaying a heat lamp on its surface. The mill contents were discharged inthe dry box to a 12 mesh sieve and pan. No agglomeration of the productwas observed. The steel balls were separated from the product on thesieve. A total of 76.4 g of black powder product was obtained.

Ball Milling of Cs/P₇

Example X (Reference No. 115, Table XIV)

Under nitrogen in a dry box, a baffled stainless steel ball millcontaining 450 g 1/4" and 450 g 1/8" stainless steel balls was chargedwith 12.12 g (0.0912 mole) of 99.98% pure Cs (from Alfa/Ventron Corp.)and 19.77 g (0.638 mole) of 99.999% pure red P (from Johnson MattheyChemicals). The mill was sealed and rotated on a roll station for 46.5hours at ambient temperature. (no external heat source applied). Uponopening the mill in the dry box, almost total agglomeration of theproduct was observed on the mill walls. This material was scraped offwith a spatula and discharged to a 12 mesh sieve and pan. The chunks ofproduct were then crushed through the sieve. A total of 27.8 g ofproduct was collected in the pan.

Table XIV summarizes the results of milling various metals with redphosphorus. As previously noted, these materials are surprisinglystable.

    TABLE XIV      MILLING OF METALS WITH RED PHOSPHORUS  *MODE OF CHARGE WEIGHT AND     TOTAL MILLING   REF. NO. MILLING RATIO (ATOM) REAGENT PURITY REAGENT     SUPPLIER TIME (HRS) TEMPERATURE RESULTS       80 BM(a,e) K/P.sub.125 0.15 g K-reagent grade J. T. Baker 42.0 ambient 1     2.6 g powder-    15 g P-reagent grade J. T. Baker   no agglomeration 81     BM(a,e) K/P.sub.30 1.00 g K-reagent grade J. T. Baker 50.0 ambient 22.7     g powder-    23.8 g P-reagent grade J. T. Baker   slight agglomeration     82 BM(a,e) K/P.sub.15 1.69 g K-reagent grade J. T. Baker 41.0 ambient     19.7 g powder-no    20 g P-reagent grade J. T. Baker   agglomeration 83     BM(a,e) K/P.sub.15 4.20 g K-reagent grade J. T. Baker 94.5 ambient 52.4     g powder-slight    50 g P-reagent grade J. T. Baker   agglomeration 84     BM(a,e) K/P.sub.15 4.20 g K-reagent grade J. T. Baker 66.0 98°     C.(66 hrs) 49.9 g powder-no    50 g P-reagent grade J. T. Baker     agglomeration 85 BM(a,e) K/P.sub.15 2.68 g K-99.95% United Min.-Chem     94.5 108° C.(3.5 hrs) 28.6 g powder-1.8 g    31.8 g P-99.9999%     Johnson Matthey   unmilled P-no        agglomeration 86 BM(a,e) K/P.sub.1     5 4.20 g K-reagent grade J. T. Baker 43.5 75° C.(43.5 hrs) 52.6 g     powder-no    50 g P-reagent grade J. T. Baker   agglomeration 87 BM(a,e)     K/P.sub.15 4.20 g K-reagent grade J. T. Baker 88.0 75° C.(65.5     hrs) 54.0 g powder-no    50 g P-reagant grade J. T. Baker   agglomeration      88 BM(a,e) K/P.sub.15 6.14 g K-99.95% United Min-Chem 71.0 100°     C.(4 hrs) 76.4 g powder    72.95 g P-99.9999% Johnson Matthey 89 BM(c)     K/P.sub.15 6.14 g K-reagent grade J. T. Baker 41.5 100° C.(3 hrs)     154.8 g powder    72.95 g P-reagent grade J. T. Baker   (0.43 g unmilled     K) 90 BM(c,d) K/P.sub.15 5 g K-reagent grade J. T. Baker 46.5 100°      C.(4 hrs) 63 g powder-no    59.4 g P-reagent grade J. T.Baker     agglomeration 91 BM(b,e) K/P.sub.11 4.89 g K-99.95% United Min-Chem 79.0     100°      C.(1 hr) 44.6 g powder-no    42.61 g P-about 99.95% Atomergics     agglomeration     Chemetals 92 BM(c,d) K/P.sub.7 5 g K-reagent grade J.     T. Baker 49.0 100° C.(3 hrs) 30.2 g powder crush-    27.72 g     P-reagent grade J. T. Baker   ed thru 12 mesh sieve-        severe     agglomeration 93 BM(b,d) K/P.sub.7 7 g K-reagent grade J. T. Baker 69.0     100° C.(3 hrs) 43.7 g agglomeration?    38.8 g P-reagent grade J.     T. Baker 94 Bm(b,e) K/P.sub.7 10 g K-reagent grade J. T. Baker 48.5     100° C.(4 hrs) 62.6 g crushed thru    55.45 g P-about 99.95%     Atomergic   12 mesh sieve-     Chemetals   considerable agglom-     eration 95 BM(b,d) K/P.sub.7 5.18 g K-99.95% Alfa/Ventron 48.0 100.degree     . C.(3 hrs) 29.7 g crushed thru    28.72 g P-99.999% Johnson Matthey     12 mesh sieve-severe        agglomeration96 BM(b,e) K/P.sub.5 8 g     K-reagent grade J. T. Baker 52.0 100° C.(3 hrs) 36.2 g crushed     thru    31.68 g P-approx. Atomergic   12 mesh sieve-severe    99.95%     Chemetals   agglomeration 97 BM(a,e) K/As.sub.2      /P.sub.13 2.5 g K-reagent grade J. T. Baker 66.5 101° C.(66.5     hrs) 36.0 g powder-no    9.58 g As-99.9% Alfa/Ventron   agglomeration     24.74 g P-reagent grade J. T. Baker 98 BM + CM + VM K/As.sub.4 /P.sub.11     3.35 g K-99.95% Alfa/Ventron (1) 285 BM 100° C.(2.5 hrs) As did     not mill  (b,e) (a,e)  25.68 g As lump-99.9999 Johnson Matthey (2) 94 VM     ambient As still did not mill    29.19 g P-99.999% Johnson Matthey (3)     separated out As 4, 2 min. cycles As finally divided      & cryomilled     at-196° C.      (Spex Mill) (CM)      (4) recombine & ambient no     agglomeration      ball mill      50 hrs 99 BM(c,d) K/As.sub.7 /P.sub.7     2.5 g K-reagent grade J. T. Baker 68.5 approx. 100° C. powder- no        33.53 g As powder-99.9% Alfa/Ventron  (3 hrs) agglomeration    13.86     g P-reagent grade J. T. Baker 100  BM K/Bi.sub.2 /P.sub.13 2.16 g     K-99.95% Alfa/Ventron 133.0 approx. 46.4 g crushed thru    23.08 g     Bi-99.9999% Alfa/Ventron  100° C.(3 hrs) 12 mesh sieve-con-     22.23 g P-99.9999% Johnson Matthey   siderable agglomera-        tion     101  BM(b,d) K/Sb.sub.2 /P.sub.13 3.18 g K-99.95% Alfa/Ventron 115.5     ambient 54.4 g powder-no    19.80 g Sb-99.9999% Alfa/Ventron   agglomerat     ion-some     (-100 mesh)   shock sensitivity    32.74 g P-99.999%     Johnson Matthey 102  BM(a,e) Na/P.sub.15 l g Na-reagent grade J. T.     Baker 72.0 106° C.(23 hrs) 19.6 g powder (no    20.2 g P-reagent     grade J. T. Baker   agglomeration) 103  BM(d) Na/P.sub.15 1.92 g     Na-99.95% Alfa/Ventron 88.0 approx. 100° C. 39.3 g powder (no     38.8 g P-99.999% Johnson Matthey  (6.5 hrs) agglomeration) 104  BM(b)     Na/P.sub.11 5.89 g Na-99.95% United Min-Chem 108.5 approx. 100°     C. 91.5 g powder (no    87.28 g P-approx. Atomergic  (4 hrs) agglomeratio     n)    99.95% Chemetals 105  BM(b) Na/P.sub.7 6.28 g Na-99.95% United     Min-Chem 70.0 ambient 63.9 g powder (no    59.21 g P-approx. Atomergic     agglomeration)    99.95% Chemetals 106  BM(a,e) Li/P.sub.19.05 0.8 g     Li-99.9% Alfa/Ventron-rod 67.5 approx. 100° C. 52.5 g powder     (0.17 g    53.56 g P-reagent grade J. T. Baker  (67.5 hrs) unmilled Li)     107  BM(b) Li /P.sub.9.65 1.6 g Li-99.9% Alfa/Ventron- 70.0 ambient     50.36 g powder (0.44 g     (shot)   unmilled Li)    49.99 g P-approx.     Atomergic    99.95% Chemetals 108  BM(a,e) Rb/P.sub.15 5.56 g Rb-99.93%     Alfa/Ventron 69.0 ambient powder (no    30.22 g P-reagent grade J. T.     Baker   agglomeration) 109  BM(a,e) Rb/P.sub.15 5.74 g Rb-99.93%     Alfa/Ventron 115.5 ambient 35.7 g powder (no    31.2 g P-99.999% Johnson     Matthey   agglomeration) 110  BM(b,e) Rb/P.sub.7 11.22 g Rb-99.93%     Alfa/Ventron 48.0 ambient 36.2 g crushed thru    28.46 g P-99.999%     Johnson Matthey   12 mesh sieve-almost        total agglomeration 111     BM Cs/P.sub.15 14.47 g Cs-99.98% Alfa/Ventron 47.5 ambient 60.2 g     crushed thru    50.58 g P-99.9999% Johnson Matthey   12 mesh sieve-con-           siderable agglomera-        tion 112  BM(b,d) Cs/P.sub.15 5.82 g     Cs-99.98% Alfa/Ventron 67.0 ambient 23.76 g powder (no    20.34 g     P-99.999% Johnson Matthey   agglomeration) 113  BM(b,d) Cs/P.sub.7 12.30     g Cs-99.98% Alfa/Ventron 48.0 ambient 29.1 g crushed thru    20.06 g     P-99.999% Johnson Matthey   12 mesh sieve-severe        agglomeration     114  BM(b,d) Cs/P.sub.7 12.36 g Cs-99.98% Alfa/Ventron 88.5 ambient 26.5     g crushed thru    20.16 g P-99.999% Johnson Matthey   12 mesh sieve-sever     e        agglomeration 115  BM(b,d) Cs/P.sub.7 12.12 g Cs-99.98%     Alfa/Ventron 46.5 ambient 27.8 g crushed thru    19.77 g P-99.999%     Johnson Matthey   12 mesh sieve-almost        100% agglomerated     (BM) Ball Milling     (CM) Cryo Milling     (VM) Vibratory Milling

Analysis of Products

Table XV summarizes the various MP_(x) (X=15 and x much greater than 15,the new form of phosphorus) materials synthesized from vapor transportwith one source (1S-VT), from vapor transport with two source (2S-VT),condensed phase processes and chemical vapor deposition (CVD).

                  TABLE XV                                                        ______________________________________                                        MP.sub.x M = Li, Na, K, Rb, Cs                                                X              X = 15   X much greater than 15                                ______________________________________                                        1S-VT   single     X        X                                                         crystals                                                                      poly.               B, TF                                                     amorphous           B                                                 2S-VT   single                                                                        crystals                                                                      poly.      TF       TF                                                        amorphous  TF       B                                                 Condensed                                                                             single     X                                                          Phase   crystals                                                                      poly.      B*                                                         C V D   amorphous  TF                                                         ______________________________________                                         X = crystals/whiskers                                                         B = Bulk greater than 10 micrometers thick                                    TF = Thin film less than 10 micrometers thick                                 B* = Powder                                                              

The materials obtained from these techniques were crystals or whiskers,referred to as X; solid polycrystalline bulk, referred to as B; solidthin film, referred to as TF; solid amorphous, referred to as B and TF;and bulk powder from condensed phase synthesis referred to as B*.

The analysis of MP₁₅ crystalline materials was given above withreference to FIGS. 7-10. As indicated in Table XV, the polycrystallineand amorphous MP₁₅ materials have only been produced in the form of thinfilms.

Polycrystalline bulk and thin films of KP_(x) (x much greater than 15)were obtained by vapor transport (one source and two sources). Thesepolycrystalline thin films nucleate on a glass substrates (or glasswalls) and show dense packing of parallel whiskers growing perpendicularto the substrate. SEM photomicrographs, FIGS. 18, 19, and 20 of suchmaterials show a large physical separation between the KP_(x) whiskers.

These polycrystalline thin films are formed at low temperatures fromaround 455° C. to 375° C. where the amorphous phase begins to form.

Analysis on these materials wet chemical, XRD and EDAX consistently showx to be much greater than 15 (typically greater than 1000). A typicalpowder XRD diagram fingerprint of crystalline MP_(x) (x much greaterthan 15) is shown in FIG. 10.

As indicated in Table XV, amorphous MP_(x) materials can be formed inbulk form (boules) by the vapor transport techniques. These boules areformed in the narrow end 160 of tube 32 (FIGS. 1 and 2), the narrow end162 of tube 58 of FIG. 3, or as pieces of material in zone 2 of FIG. 16.These materials show no X-ray diffraction peaks.

XRD powder diagrams were used in our study to characterize the degree ofamorphicity of the materials obtained by these techniques. Theseamorphous MP_(x) materials where x is much greater than 15 can be cut,lapped and polished using conventional semiconductor techniques forwafers processing. This is even true of material containing no more than50 to 500 parts per million of M, a new form of phosphorus.

The resulting high x, KP_(x) amorphous wafers or substrates were shownto have useful semiconductor properties with electro-optical responsealmost identical with whiskers of KP₁₅. We therefore conclude that thelocal order of all MP_(x) materials where x=15 or is very much greaterthan 15 (when solidified in the presence of alkali metal) exhibit thesame local order substantially throughout their extent. This local orderis the all parallel pentagonal phosphorus tubes.

Amorphous high x, KP_(x) materials were prepared with mirror finishsurfaces for electro-optical evaluation. Routine surface preparation ofthese amorphous materials includes several processing steps such ascutting, embedding, lapping polishing and chemical etching. Surface workdamage induced during such processing steps are known to affect theelectro-optical performance of semiconductor materials. Therefore,attention was focused on assessing techniques and processing stepsleading to a "damage free" surface. The following processing steps havebeen found to be suitable for the preparation of high quality mirrorfinish surfaces.

Embedded boules of high x, KP_(x) (about 1 to 2 cm in length) from TableVII were cut with a slow speed diamond saw using minimum pressure. Eachwafer was sliced to a thickness of approximately 1 mm. The wafer wasthen immersed in a bromine/HN0₃ solution. To remove sufficient cuttingdamage the thickness of each wafer was reduced by this chemical etchingby approximately 50 micrometers. The wafers were then washed and checkedfor inclusions and voids. The high x, KP_(x) amorphous material appearsto be void free.

A standard low temperature wax (melting point about 80° C.) was used tomount the high x, KP_(x) wafers onto a polishing block. The wafers werethen lapped at 50 rpm at 2 minute intervals individually with a 400 and600 SiC grit using distilled water as a lubricant with a 50 g/cm² weightuntil a smooth surface was achieved.

The final polishing step was carried out for one hour at 50 rpm with 50g/cm² weight on a Texmet cloth with 3 micrometers diamond compound andlapping oil as extender. This polishing step was followed by anadditional fifteen minute polishing step at 50 rpm with 50 g/cm² weighton a microcloth with a slurry of 0.05 micrometers of gamma aluminasuspension in distilled water. All procedures require scrupulous inbetween cleaning steps in a sonic bath with subsequent rinsing anddrying.

Samples prepared by this technique have a high quality mirror finishsurface. The final polishing step was performed on standardmetallographic Buehler polishing equipment.

Chemical etching plays a prominent role in wafer preparation, surfacetreatment, pre-device preparation, metallization and device processing.

Numerous review articles are available covering the chemistry and thepractical aspects of etching processes. However, most information onspecific etchants is widely scattered throughout the scientificliterature. An attempt was made to bring together essential informationthat should be useful to the selection of an etching process relevant tothese amorphous high x materials. Special attention was placed onetching procedures and processes used for surface preparation. It wasfound that some of the etching solutions and procedures currently usedfor GaP and InP are applicable but with different etching rates.

The following etching solutions were selected and tested:

5-10% Br₂ 95-90% CH₃ OH for general etching and polishing

1% Br₂, 99% CH₃ OH for polishing high quality surface (approximately 1micron/minute)

5% by weight NaOCl solution for chemical polishing

1 HCl:2 HNO₃ ; (1% Br₂) for removing work damage after cutting andlapping

1 HCl:b 2 HNO₃ for removing surface layer.

Several samples were prepared for optical absorption measurements. Theabove technique was used to slice and polish on both sides amorphouswafers of high x material as thin as 0.5 mm. Reference samples of GaPand GaAs crystals were also polished on both sides and used to measurethe band gap by optical absorption.

Etching techniques were developed to reveal microstructures and to thindown small areas to 0.2 mm thick for optical absorption.

Several etching solutions were selected and tested. The best chemicalsolution was found to be a mixture of 6.0 g potassium hydroxide, 4 g redpotassium ferric cyanide and 50 ml distilled water at 70° C. Applicationto reveal an etching pattern takes less than 60 seconds. This solutionis very stable and can be used with reproducible etching rates.

After embedding, cutting and polishing, several samples of amorphousKP_(x) (x much greater than 15) from Tables VII and VIII have beenetched. Typical microstructures were revealed from this chemical etchingtreatment after 30 seconds.

FIG. 21 is a photomicrograph at 360 magnification of the etching patternon a surface cut perpendicular to the axis of an amorphous boule of highx material grown by single source vapor transport (Reference No. 28,Table VII) showing honeycomb microstructures with well defined domains afew microns in size. These honeycomb microstructures are characteristicfor an etching pattern on a material having a two dimensional atomicframework (such as parallel tubes).

FIG. 22 is a photomicrograph at 360 magnification of the etching patternon a surface cut perpendicular to the axis of growth of the amorphoushigh x material grown by two source vapor transport in Example VI. FIG.23 is a photomicrograph of the same etched surface as shown in FIG. 22at 720 magnification.. FIG. 24 is a photomicrograph at 360 magnificationof an etched surface perpendicular to the surface shown in FIGS. 22 and23 and shows an etching pattern characteristic of tubular packing.

Thus we conclude from the available evidence that our MP_(x) materialswhere M is an alkali metal where x is much greater than 15, i.e. wherethe amount of alkali metal is as little as 50 parts per million all haveas their local order the all parallel pentagonal phosphorus tubes eitherall parallel (the MP₁₅ form) or double alternating perpendicular layer(monoclinic phosphorus).

Electro-Optical Characterization of High Phosphorus Materials from OneSource Vapor Transport

The electro-optical characterization was carried out on single crystalwhiskers, on polycrystalline films, and amorphous films and boules. Thecharacterization consists of (1) optical measurements on samples with noelectrical contacts (absorption edge, photoluminescence) (2) electricalmeasurements with simple contacts of linear behavior (conductivity,temperature dependent conductivity, photoconductivity, wavelengthdependence of photoconductivity, conductivity type) (3) electricalmeasurements with non-linear or rectifying contacts with metals whichare indicative of the semiconducting behavior.

From the above data we extracted the properties which indicate that allmaterials produced have electrical criteria for useful semiconductors,that is, they all have an energy band gap from 1-3 eV; conductivitybetween 10⁻⁵ -10⁻¹² (ohm-cm)⁻¹ ; a photoconductivity ratio from 100 to10,000, and chemical and physical stability under ambient operatingconditions.

Measurements were carried out on the following equipment:

    ______________________________________                                        (1) Absorption edge Zeiss 2 beam IR and visible                                                   spectrometer                                                  Photoluminescence                                                                             Low temperature (4° K.) cryostat                                       and laser excitation                                      (2) Conductivity    2 probe and 4 probe measurements                              Temperature Depen-                                                                            from 300° K. to 550° K. in an                   dent conductivity                                                                             evacuated chamber                                             Photoconductivity                                                                             with light source of                                                          approximately 100 mW/cm.sup.2                                 Wavelength dependent                                                                          Xe lamp light source and mono-                                photoconductivity                                                                             chromator                                                     Conductivity type                                                                             thermoelectric power measurement                                              with hot and cold probes                                  (3) wet silver paint was used to provide a temporary                              junction to materials, with a photovoltaic open voltage                       of 0.2 V measured under illumination.                                     ______________________________________                                    

Metallic and pressure contacts forming junctions were evaluated fortheir current voltage characteristics on a Tektronix curve tracer.

Data on samples from the broad class of materials under investigation issummarized in Tables XVI, XVII, XVIII and XIX.

Table XVI summarizes the basic physical, chemical and electro-opticalproperties of the prototype material namely KP_(x) x ranging from 15 tomuch greater than 15, in various physical forms and chemicalcomposition.

                                      TABLE XVI                                   __________________________________________________________________________    Typical data on material obtained by single source vapor transport from       K/P.sub.15 starting charge                                                                               POLYCRYSTALLINE (KP.sub.x)                                                                   AMORPHOUS (KP.sub.x)                PROPERTIES   SINGLE CRYSTAL (KP.sub.15)                                                                  x much greater than 15                                                                       x much greater than                 __________________________________________________________________________                                              15                                  Electro-Optical                                                               Conductivity 10.sup.-7 -10.sup.-8                                                                        10.sup.-7 -10.sup.-8                                                                         10.sup.-8                           (ohm-cm).sup.-1                                                               Photoconductivity                                                                          10.sup.2 -10.sup.4                                                                          10.sup.2       10.sup.2                            (Light/Dark) (ratio)                                                          Photoconductivity                                                                          1.4-1.8 eV    1.4-1.8 eV     1.4-1.8 eV                          Peak at                                                                       Activation Energy                                                                          1.2 eV        1.4 eV         1.6 eV                              (2 Eg) from temp-                                                             erature dependence                                                            of conductivity                                                               Absorption   1.8 ev        1.4 ev         --                                  Edge                                                                          Luminescence,                                                                              1.8 eV        --             --                                  4° K.                                                                  Luminescence,                                                                              1.7 eV        1.7 eV                                             300° K.                                                                             --            n-Type         n-Type                              Type         --            0.2 eV         --                                  Photovoltaic                                                                  (Open Circuit                                                                 Voltage)                                                                      Thermal                                                                       DTA Sharp endotherm                                                                        630° C.-first heat                                                                   615-first heat 590-first heat                                   630° C.-second heat                                                                  590-second heat                                                                              590-second heat                     TGA          450° C.                                                                              --             --                                  Decomposition                                                                              450° C.                                                                              --             --                                  Temperature                                                                   (Mass Spectrometer)                                                           400° C./3 hrs.                                                                      Stable up to 450° C.                                                                 Stable up to 400° C.                                                                  Stable up to 350° C.         Chemical Reagent                                                              Room Temp.-3 hrs.                                                             85% H.sub.3 PO.sub.4, 95% H.sub.2 SO.sub.4                                                 Stable        Stable         Stable                              50% HF, 37.5% HCl,                                                                         Stable        Stable         Stable                              50% NaOH                                                                      Boiling H.sub.2 O 1 hr.                                                                    Stable        Stable         Stable                              __________________________________________________________________________     Stability is based upon visual inspection.                                    (DTA) Differential thermal analysis                                           (TGA) Thermal gravimetric analysis                                       

Table XVII shows the properties of Group 1a (alkali metal)polyphosphides of various compositions and physical form. We observedthat the electro-optical properties are independent of the metal whetherit be Li, Na, K, Rb, Cs; physical form--crystal, polycrystal, amorphous(boule or film); and chemical composition, x=15 or much greater than 15.

                                      TABLE XVII                                  __________________________________________________________________________    Polyphosphide - structural and electro-optical properties                                      X-RAY                                                                         POWDER             PHOTO-                                             CHEMICAL                                                                              DIFFRACTION                                                                            CONDUCTIVITY                                                                            CONDUCTIVITY                                                                            BANDGAP                         MATERIALS                                                                              ANALYSIS                                                                              PATTERN  (OHM-CM).sup.-1                                                                         RATIO     (eV)                            __________________________________________________________________________    M = K                                                                         crystalline                                                                            KP.sub.15                                                                             A        10.sup.-8 -10.sup.-9                                                                    10.sup.2 -10.sup.3                                                                      1.8                             polycrystalline                                                                        KP.sub.x x >> 15                                                                      B        10.sup.-7 -10.sup.-9                                                                    10.sup.2  1.8-2.0                         amorphous                                                                              KP.sub.x x >> 15                                                                      amorphous                                                                              10.sup.-8 -10.sup.-9                                                                    10.sup.2  1.8-2.0                         M = Na                                                                        crystalline                                                                            NaP.sub.15                                                                            A        10.sup.-8 10.sup.2  1.8                             polycrystalline                                                                        NaP.sub.x x >> 15                                                                     B        10.sup.-7 10.sup. 1 -10.sup.2                                                                     1.8                             amorphous                                                                              NaP.sub.x x >> 15                                                                     amorphous                                                                              10.sup.-7 -10.sup.-9                                                                    10.sup.3  1.8                             M = Rb                                                                        crystalline                                                                            RbP.sub.15                                                                            A        10.sup.-7 -10.sup.-8                                                                    10.sup.2  1.8                             polycrystalline                                                               amorphous                                                                     M = Cs                                                                        crystalline                                                                            CsP.sub.15                                                                            A        10.sup.-8 10.sup.2  1.8                             polycrystalline                                                               amorphous                                                                     __________________________________________________________________________     A = pattern similar to KP.sub.15                                              B = pattern similar to KP.sub.x where x is much greater than 15          

Table XVIII summarizes the properties of mixed polyphosphides and showsthose formed of mixed alkali metals have no substantial changes inproperties; partial substitution of As on P sites is possible andproduces a reduction in resistivity and possibly in the band gap (i.e.substitutional doping).

                                      TABLE XVIII                                 __________________________________________________________________________    Mixed Polyphosphides - electro-optical properties                                    CHEMICAL                                                                             X-RAY                                                                  STARTING                                                                             POWDER                                                                              CONDUCTIVITY                                                                            PHOTOCONDUCTIVITY                                                                           BANDGAP                           MATERIAL                                                                             CHARGE PATTERN                                                                             (OHM-CM).sup.-1                                                                         RATIO         eV                                __________________________________________________________________________    K.sub.y Na.sub.1-y P.sub.x                                                           K.sub.12 /Na/P.sub.160                                                               A     10.sup.-8 -10.sup.-9                                                                    10.sup.2      1.8-2                             crystalline                                                                   K.sub.y Li.sub.1-y P.sub.x                                                           K.sub.6 /Li.sub.2 /P.sub.80                                                          A     10.sup.-9 10.sup.2      1.8                               crystalline                                                                   Na.sub.y Rb.sub.1-y P.sub.x                                                   crystalline                                                                          Na/Rb/P.sub.30                                                                       A     10.sup.-8 10.sup.2      1.8                               amorphous                                                                            Na/Rb/P.sub.30                                                                       amorphous                                                                           10.sup.-9 10.sup.2      1.8-2                             K.sub.y As.sub.z P.sub.x-z                                                    crystalline                                                                          K/As.sub.2 /P.sub.13                                                                 A     10.sup.-9 10.sup.       1.8                               amorphous                                                                            K/As.sub.2 /P.sub.13                                                                 amorphous                                                                           10.sup.-7 10.sup.2      approx. 1.6                       K.sub.y As.sub.z P.sub.x-z                                                           K/As.sub.11 /P.sub.4                                                                 A     10.sup.-9 10.sup.2      1.8                               crystalline                                                                   __________________________________________________________________________     A = pattern similar to crystalline KP.sub.15                             

Table XIX summarizes materials and properties obtained from differentstarting charge ratios. We find that the best properties are obtainedwith materials formed from starting charge proportions of P to K ofabout 15 (i.e. between 10 to 30). Below 10 the yield decreases; above 30the physical properties of the amorphous boules begin to deteriorate.

                                      TABLE XIX                                   __________________________________________________________________________    KP.sub.x from different starting charges analyzed                             in Tables IX, X, and XI above                                                                X-RAY           PHOTO-                                         STARTING                                                                              CHEMICAL                                                                             POWDER                                                                              CONDUCTIVITY                                                                            CONDUCTIVITY                                   CHARGE  ANALYSIS                                                                             PATTERN                                                                             (ohm-cm).sup.-1                                                                         RATIO                                          __________________________________________________________________________    K/P.sub.15 reagent                                                            crystalline                                                                           x = 15 A     10.sup.-8 -10.sup.-9                                                                    10.sup.2 -10.sup.3                             polycrystalline                                                                       x >> 15                                                                              B     10.sup.-7 -10.sup.-9                                                                    10.sup.2                                       amorphous                                                                             x >> 15                                                                              amorphous                                                                           10.sup.-8 -10.sup.-9                                                                    10.sup.2                                       K/P.sub.15 pure                                                               crystalline                                                                           x = 15 A     10.sup.-9 10.sup.2                                       polycrystalline                                                                       x >> 15                                                                              B     10.sup.-8 10.sup.2                                       amorphous                                                                             x >> 15                                                                              amorphous                                                                           10.sup.-8 10.sup.3                                       K/P.sub.30                                                                    crystalline                                                                           x = 15 A     10.sup.-9 10.sup.2                                       polycrystalline                                                                       x >> 15                                                                              B     10.sup.-9 10.sup.2 -10.sup.3                             amorphous                                                                             x >> 15                                                               K/P.sub.5                                                                     crystalline                                                                           x = 15 A     10.sup.-9 10                                             polycrystalline                                                                       x >>  15                                                                             B     10.sup.-8 10                                             amorphous                                                                     K/P.sub.125                                                                   crystalline                                                                   polycrystalline                                                               amorphous                                                                             x >> 15      poor physical                                                                 properties                                               __________________________________________________________________________     A = pattern similar to crystalline KP.sub.15                                  B = pattern similar to crystalline KP.sub.x                              

We conclude that all these materials in whatever form have a band gapbetween 1 and 3 eV, more particularly in a range from 1.4 to 2.2 eV,since 1.4 eV is the lowest photoconductivity peak we measured and 2.2 eVis the estimated band gap of red phosphorus. The data further indicatesthat the band gap of the best form of these materials is approximately1.8 eV. Furthermore, their surprising high photoconductivity ratios offrom 100 to 10,000 indicate that they are very good semiconductors.

Doping

Bulk amorphous MP_(x) boules obtained by single source vapor transport(Tables VI, VII, X and XI above) in our three zone furnace having acomposition x much greater than 15 can be processed by cutting, lapping,polishing and etching into high quality, mirror finish wafers of about0.5 cm diameter.

It is on these samples that we have been able to perform electricalmeasurements with different geometrical arrangements of electricalcontacts to determine accurately the bulk conductivity of the materials.By 2 probe and 4 probe measurements, we ascertained the bulkconductivity of these materials to be 10⁻⁸ to 10⁻⁹ (ohm-cm)⁻¹. Thisconductivity is too low for the material to be able to form a sharpjunction with rectifying properties. Therefore, it was our aim to find aforeign element (dopant) which would affect the conduction mechanism inthe material and increase conductivity. As is typical of other amorphoussemiconductors, the presence of small amounts of impurities in thematerial do not affect the conductivity and, above room temperature, wefind intrinsic behavior with an activation energy equal to approximatelyhalf the bandgap, indicative of a midgap Fermi level. The lowconductivity and large photoconductivity ratio indicate a small numberof dangling bonds. This indicates that a strong perturbation of theelectronic wave function of the P--P bond will be required to modify theconductivity and conductivity type.

Two approaches were taken: (1) substitute As or Bi into the P site; (2)diffuse a foreign element into the amorphous matrix.

In the first method K/As₂ /P₁₃ has As incorporated into the matrix. Theconductivity is increased by 2 orders of magnitude (Table XVIII), andthe material remains n type.

In the second method, after trying many conventional diffusers (e.g. Cu,Zn, Al, In, Ga, KI) in vapor, liquid and solid phase diffusion with nosuccess, we found a surprising success with the diffusion of Ni and thenFe and Cr from the solid phase. For example, a layer of Ni was depositedby vacuum evaporation onto a well prepared surface of a high x, KP_(x)wafer. After annealing for several hours, the Ni was found to diffusefor about 0.5 micrometers into the substrate and the conductivityincreased by more than 5 orders of magnitude. The conductivity is stilln type.

More specifically, 1500 angstroms of Ni was deposited onto the wafer ina Varian resistance heated vacuum evaporator under pressure of 10⁻⁶Torr. The sample was sealed in an evacuated Pyrex tube and heated for 4hours at 350° C. The top Ni layer was removed. The conductivity measuredby the two probe method showed an increase from 10⁻⁸ to greater than10⁻⁴. Electro spectroscopy for chemical analysis (ESCA) depth profilingof the sample showed the diffusion depth to be 0.4 micrometers and thechemical bonding of the Ni to be Ni°, i.e. free Ni in the material. Thewavefunction of the Ni overlaps with electronic wavefunctions in theP--P matrix, affecting the conduction (mobility). The Ni concentrationis greater than about 1 atom percent.

Evaporated gold top contacts or dry silver paint in coplanar fashionform ohmic contacts to the doped layer.

Variations in the diffusion temperature show 350° C. to be optimum forNi diffusion.

Variation in the diffusion time follow the diffusion equation (diffusiondepth is proportional to square root of time) and 1500 angstroms of Niheated at 350° C. for 60 hours, showed diffusion depth of 1.5micrometers as measured by ESCA. 350° C. approaches the highesttemperature these amorphous materials may be subjected to.

Ni diffusion can also be accomplished from the liquid phase, such asfrom a Ni--Ga melt, or from the vapor phase, such as from Ni carbonylgas.

It was further found that Fe and Cr show similar behavior under theabove processing procedures.

For example, we took a cut wafer from a bulk amorphous high x bouleobtained by the single source vapor transport and evaporated 500angstroms of iron onto it and then diffused it into the wafer at 350° C.for sixteen hours. Applying two pressure probes to the doped materialgave a full non linear characteristic on the Tektronix curve tracer.

On another wafer of high x material we evaporated 300 angstroms ofnickel and 200Å of iron, then heated the wafer to 350° C. for sixteenhours. We then evaporated two 1 mm radius aluminum contacts 2000angstroms thick and measuring the current voltage characteristic withthe Tektronix curve tracer between the aluminum dots, again obtained afull non-linear characteristic.

On another wafer of high x material produced by single source vaportransport, we evaporated 500 angstroms of nichrome and then heated thewafer for diffusion at 350° C. for sixteen hours. We then evaporated twoaluminum 1 mm radius dots 2000 angstroms thick onto the wafer and againmeasured a full non-linear characteristic between the two aluminum dots.

We thus conclude that nickel, iron and chromium are useful diffusants inthese materials for lowering conductivity and that on the lowerconductivity material junctions can be effected with wet silver paint,pressure contacts and aluminum contacts.

Other elements besides Ni, Fe and Cr with occupied d or f outerelectronic levels that can overlap with the phosphorus levels areexpected to be able to affect the conductivity in these materials suchas to give p-type material and form p/n junctions for solid statedevices.

Amorphous High Phosphorus Material By Two Source Vapor Transport

Two types of materials were obtained by this method and the propertiesof these were investigated.

(1) Amorphous bulk KP_(x), (Example VI) where x equals approximately 50on one side and x is much greater than 15 on the other. Surface analysissupports the hypothesis of the template effect, which is very strong inthis instance. The surface of a cut and polished sample is of very highquality, low number of defects and voids, uniform etching pattern.

The conductivity measured was by the two probe technique 10⁻¹⁰(ohm-cm)⁻¹ and the photoconductivity ratio under illumination of 100mW/cm² is greater than 10³. The photoconductivity peak is approximatelyat 1.8 eV, indicating a bandgap of that order. The data indicates thatthe P--P bond dominates the electrical and optical properties of thismaterial as well as those in Tables XVI, XVII, XVIII and XIV, and itsstrong photoconductivity ratio is consistent with a highly reduced levelof dangling bonds.

(2) Amorphous thin films of KP₁₅, (Reference No. 47 Table XII) depositedonto glass slides which have a metal layer deposited on them for a backcontact to the thin film. The success in the thin film deposition ofKP₁₅ opens the opportunity to manufacture any types of thin filmdevices.

The amorphous KP₁₅ thin films deposited by the 2 source technique have athickness of approximately 0.5 micrometers over an area of 3 cm². Thefilm is uniform and the surface roughness does not exceed 2,000angstroms. The film is chemically stable. FIG. 25 is a photomicrographat 2000 magnification of the surface of one of these KP₁₅ films. Theadhesion to the substrate is excellent. Quantitative analysis of thefilm was performed using a Scanning Electron Microscope (SEM) and anEnergy Dispersive X-ray (EDAX) measurement The composition of the filmwas found to be in agreement with the KP₁₅ nominal compositio Theuniform composition, homogeneity, and pinhole free surface leads touniform electro-optical properties across the films.

In view of the diffusing capability of Ni into bulk amorphous KP_(x), anNi film 172 was evaporated onto the glass subsrate 170 to form a backcontact for the amorphous KP₁₅ layer 174 as shown in FIG. 26.

The Ni serves as a back contact and a diffuser. ESCA and SEM profilingshows Ni to diffuse significantly into the KP₁₅ film 174 at a rate of200 angstroms per hour during the KP₁₅ growth process.

In more detail we deposited by vacuum evaporation 1500 angstroms of Ni172 onto a glass slide 170 at 10⁻⁶ Torr. pressure. Part of the Nisurface is then masked with a Ta mask in order to have a material freezone for electrical contact.

Two micrometers of amorphous KP₁₅ 174 is deposited in our two sourceapparatus onto the Ni film 172. The composition of this film has beenidentified to be KP₁₅, it is amorphous and has more than 1% Ni diffusedinto the film.

Pressure contact with an electrical probe was applied to the top of theKP₁₅ film. The two leads, from the back contact and the top pressurecontact, were connected to a Tektronix Curve Tracer 176 to observe thecurrent voltage characteristics. The forward characteristic of therectifying pressure contact junction is shown in FIG. 27, whichindicates a junction with a barrier height of 0.5 eV and current in themA range.

As shown in FIG. 28, we also deposited by vacuum evaporation a 2 mmradius Cu contact 178 onto the top surface 180 of a KP₁₅ amorphous layer182 grown by the two source technique on a Ni layer 184 deposited on aglass substrate 186. We connected the Tektronix curve tracer 176, asshown, and measured the full forward and reverse biased junction curveshown in FIG. 29, thus indicated that Cu forms junctions with thesematerials.

Subsequently, smaller metal dots were deposited as top contacts in orderto reduce the effect of leakage currents at the edges of the contacts.10⁻³ cm² area top contacts and 10⁻⁵ cm² top contacts were deposited inthe vacuum evaporator through mechanical masks. The I-V characteristicsshown in FIG. 31 were observed with Cu, Au, and Al top contacts. Theyappear as the breakdown voltages of two back to back diodes in eachinstance. Similar curves were obtained with Ni, Ti, Mg, and Ag as thetop contacts.

The most significant difference appears in the fact that Au contactschange the I-V characteristic after applying 10 V to the device. The I-Vcharacteristic become asymmetric, as shown in FIG. 32, and a more ohmiccontact is formed at the Au interface after this "forming" process. The"forming" is consistently observed with Au, and intermittently observedwith Ag and Cu top contacts. The "forming" does not permanently affectthe device, but it reappears every time a voltage is applied. Heatingthe device at 300° C. does not affect the phenomenon. Cooling the deviceto -20° C. results in very sharp I-V characteristics (FIG. 33).

It appears as if the "forming" may be a breakdown of a high resistancelayer remaining between the diffused part of the device and the topcontact. Capacitance - voltage (C-V) characteristics shown in FIGS. 34,35, and 36 point in the same direction. Al and Au top contacts have C-Vcharacteristics of double diodes, but convert into single diode behaviorin the case of Au contacts. If we assume a dielectric constant ofapproximately 10, we can extract a carrier concentration ofapproximately 10¹⁶ carriers per cm³ near the junction and a carriermobility of approximately 10⁻² to 1 cm² /volt second. Frequencydependence of the capacitance and resistance in FIG. 37 can be used tomodel the multiple junctions that can form in such a structure with agraded diffusion profile in the active material. In addition, poor bulkmaterial quality (low density) and rough surface morphology couldcontribute to the complex observations. Nonetheless, junction formationcapability on amorphous 2 source thin film KP₁₅ has been demonstrated.

Some of the above phenomena, such as "forming" with Au top contacts wasalso observed with flash evaporated thin films deposited on Ni. Thisfilm is not pure KP₁₅, but has excellent quality. No C-V dependence wasseen in this case. The device, which was very thin, had a good responseto light and a small (10⁻⁶ amps) current was drawn from it under shortcircuit conditions when illuminated with visible light.

We expect that KP₁₅ thin films made by CVD technique will result insimilar behavior when the films are sufficiently thick. At the momentthey have been too thin and have been found to short out.

The formation of junctions with these materials indicates that they maybe utilized to form pn junctions, Schottky diodes, or Metal OxideSemiconductor (MOS) devices.

We expect that by utilizing the above noted classes of dopants, that thematerials can be converted to p-type conductivity and thus will beuseful in the entire range of semiconductors.

The photoconductivity ratio was obtained in all these by forming asemiconductor device comprising our material and means attached to thematerial for electrically communicating with it. This means comprisedtwo single electrodes 80 and 82 attached to the material illustrated inFIG. 30.

More specifically, for a single crystal of MP₁₅, two copper strips 80and 82 were adhesively attached to a glass substrate 84. A sample ofKP₁₅ 86, made according to the above teachings, was bridged acrossstrips 80 and 82 at one end thereof and attached hereto by silver paint88. An electrometer attached to the opposite ends of strips 80, 82introduces an electrical potential to the KP₁₅, and thereby permitsmeasurement of the resistivity of the KP₁₅.

The resultant device of FIG. 30 and similar devices using our othermaterials established that our high phosphorus materials can in fact beused to control the flow of electrical current, at least as aphotosensitive resistor.

In addition, our materials show luminescence characteristics with anemission peak at 1.8 eV at temperatures of four degrees K, andluminescence at ambient temperatures.

Preparation of Large Crystal Monoclinic P Rubidium

We have found that the RbP₁₅ can be utilized to produce large crystalmonoclinic phosphorus.

A 0.62 g sample of RbP₁₅ encapsulated, in vacuo, in a 10 mm 0.D.×6 mmI.D.×5.0 cm quartz tube was vertically positioned in a crucible furnaceand subjected to a temperature gradient such that the RbP₁₅ charge wasmaintained at 552° C. while the top of the tube was maintained at 539°C. After heating for approximately 22 hours, the tube was opened andsingle crystals of monoclinic phosphorus, as large as 3.0 mm on edge, inthe form of truncated pyramids were found in the upper (cooler) regionof the tube.

We found that large crystal monoclinic phosphorus can also be preparedfrom mixtures of Rb and P in the atom ratio of 1 to 15 (RbP₁₅).

Cesium and Sodium

Large single crystals of monoclinic phosphorus were also grown via vaportransport using either CsP₁₅ or NaP₁₅ charges formed in our condensedphase process. In each run approximately 0.5 g of the appropriate alkalimetal polyphosphide was sealed in vacuo in a quartz tube (10 mm 0.D.×6mm I.D.) of length 8.9 cm. The tubes were then subjected to atemperature gradient such that the alkali metal polyphosphide chargeswere maintained at 558° C. while the tops of the tubes were maintainedat 514° C. After 48 hours, large deep-red crystalline stacked squareplatelets of monoclinic phosphorus formed from the CsP₁₅ charges.

The morphologies of the monoclinic phosphorus crystals grown from CsP₁₅and NaP₁₅ condensed phase charges appear to be very similar, that is,stacked square platelets. This is in contrast to the truncated pyramidalhabit of the monoclinic phosphorus crystals grown from a RbP₁₅ charge.

We found that large crystal monoclinic phosphorus can also be preparefrom Cs/P₁₁, and Cs/P₁₁ and Cs/P₁₅ mixtures maintained at hightemperatures.

Potassium

Using similar processes we have also produced monoclinic phosphoruscrystals from condensed phase KP₁₅, and from mixtures of K/P₃₀ andK/P₁₂₅.

Lithium

No experiments have been conducted with lithium/phosphorus charges.However, we expect that large crystal monoclinic phosphorus can beprepared from the materials under similar conditions.

Effect of Temperature

While the nature of the alkali metal present seems not to be important,the temperature at which the charge is maintained is apparently veryimportant to the crystal growth process. In the case of the Cs/P₁₁ ballmilled system, large crystals were produced in experiments where thecharge was maintained at 555° C. and 554° C. However, in experimentswhere the charge was held at 565° C. and 545° C., no large monocliniccrystals were produced.

Referring to FIG. 38, using our preferred apparatus, we sealed a 0.6 gmsample of RbP₁₅ prepared by our condensed phase process in vacuo in a 12mm 0.D.×6 mm I.D.×8 cm long glass tube 270. The top was sealed with a 16mm diameter flat glass surface 272. Fill tube 274 is provided with aconstriction 276 at which it is sealed after charging and evacuation.

The tube was subjected to a temperature gradient such that the flatsurface 272 at the top of the tube was maintained at 462° C., while thecharge at the bottom of the tube was maintained at 550° C. After heatingfor 140 hours approximately half of the original charge had beentransported to the flat surface.

The resulting button-like boule was cleaved and examined. It was made upentirely of uniform light-red fibers--not the desired large crystalmonoclinic phosphorus. FIGS. 44 and 45 are SEM photomicrographs of thisproduct at 200 and 1000× magnification respectively.

The SEM photomicrographs of FIGS. 44 and 45 proved to be a surprise. Theindividual "fibers" consist of bundles of long platelets which areattached such that they appear to be star-shaped rods when viewed fromthe end. This material is thus quite different in appearance from the"twisted tube" fibrous phosphorus produced via vapor transport from a99.9999% red phosphorus charge (see below).

We conclude that the condensing temperature to form large crystalmonoclinic phosphorus should be in the range of 500° to 560° C. Furtherexperiments indicate that the preferred condensing temperature is about539° C.

The charge must be heated to a temperature above 545° C. and below 565°C. as previously indicated. Our preferred range is 550° to 560° C. withabout 555° C. giving the best results.

Effect of Composition

We have produced monoclinic phosphorus from charge ratios of P to alkalimetal of 11 to 125. However a ratio of about 15 seems to work best.

Characteristics of Monoclinic Phosphorus Condensed from Vapor in thePresence of an Alkali Metal

FIG. 39 is a photomicrograph at 50× magnification showing a pyramidallyshaped monoclinic crystal of phosphorus prepared from a RbP₁₅ charge.These crystals are hard to cleave Similar crystals are produced fromcharges utilizing sodium as the alkali metal We have produced crystalsas large as 4×3×2 mm.

FIG. 40 is a photomicrograph, at 80× magnification, of a crystal ofmonoclinic phosphorus produced from a ball milled mixture of Cs/P₁₁.These platelets are easy to cleave into mica-like sheets. Similarcrystals can be produced from a charge of K/P₁₅. We have producedcrystals in this habit as large as 4 mm on a side and 2 mm thick.

We have determined that the crystals are birefringent. When placedbetween crossed polarizers in a polarizing microscope, they rotate thelight and allow some of it to pass through. Thus they may be utilized asbirefringent devices such as optical rotators in the red and infra-redportion of the spectrum.

Chemical analysis indicates that they contain anywhere from 500 to 2000parts per million of an alkali metal. They are made in a process whichtakes as little as 22 hours versus the 11 days employed in the processof the prior art to produce Hittorf's phosphorus.

The powdered X-ray diffraction pattern of these crystals is consistentwith that of the prior art Hittorf's phosphorus.

The photoluminescence spectra shown in FIGS. 41 and 42 were taken withan Argon laser Raman spectrometer. A broad peak at 1.91 eV is clearlyobserved with a half width of about 0.29 eV. This indicates a band gapof about 2.0 eV at room temperature.

The FIG. 41 spectrum was taken utilizing a monoclinic crystal ofphosphorus prepared in the presence of cesium while the FIG. 42 spectrumwas taken using monoclinic phosphorus condensed in the presence ofrubidium.

The Raman spectrum of FIG. 43 was taken utilizing a monoclinicphosphorus crystal formed in the presence of Rubidium. The peaks 280,282, 283, 284, and 285 are at wave numbers 285, 367, 465, 483, and 529.

Evaporated dots about 25 micrometers in diameter were deposited on largecrystals of monoclinic phosphorus (from a Rb/P₁₅ source) for electricalmeasurements. The resistance of the crystals was found to be 10⁶ ohm to10⁷ ohm and practically independent of the geometry of the crystal andthe size of the contacts. This reflects surface resistance.

These crystals may be utilized as the substrate for depositing 3-5materials such as Indium Phosphide or Gallium Phosphide. They may beutilized as phosphors in luminescent displays, semiconductors, lasers,and as starting materials for other semiconducting devices.

Twisted Fiber Phosphorus

The presence of the alkali metal in the charge appears to be critical tothe production of large crystal monoclinic phosphorus. We attempted toproduce large single crystals of monoclinic phosphorus from 99.9999%pure red phosphorus by mimicking the conditions used successfully withthe various alkali metal/phosphorus systems. This attempt failed. Nomonoclinic phosphorus was produced. For example, a 0.6 g sample of99.9999% pure red phosphorus was heated at 552° C. in a sealed evacuatedtube in a vertically positioned 10 mm outside diameter×6 mm insidediameter quartz tube. The temperature gradient between the bottom andtop of the two and three-quarter inches long tube was 43° C. Afterheating for 24 hours, more than half of the charge had been transportedto the top third of the tube where a boule had formed.

Surprisingly, the boule was found to consist entirely of a red fibrousmaterial. Several long (approximately 1.5 mm) fibers were found in thevapor space at the bottom of the boule. Microscopic examination of thedeep red fibers. revealed that they are twisted.

XRD data secured on the fibrous material was found to match that securedearlier on polycrystalline KP_(x) where x is much greater than 15. FIG.46 is an SEM photomicrograph at 500 magnification of these fibers.

Differential thermal analytical data was found to be similar to thatsecured on polycrystalling high x material. For two DTA determinations,the first heat plot consists of a single endotherm at 622° C. (average).The second heat plot consists of a single endotherm in both cases at599° C. The DTA data secured earlier on polycrystalline high x materialconsists of a first heat single endotherm--at 614° C. and a second heatsingle endotherm--at 590° C. Thus, we observed substantial similaritiesbetween the fibrous phosphorus prepared from 99.9999% red phosphorus andpolycrystalline high x material.

Flash Evaporation

We have succeeded in forming stable thin film amorphous coatings onglass and nickel coated glass substrates using a flash evaporationprocess. The flash evaporation apparatus is generally indicated at 302in FIG. 47. It comprises a glass cylinder 304 connected to a vacuumsystem (not shown) through tubing 306. Argon is supplied at inlet 308 ofsupply tube 310. Reservoir 312 is filled with powdered KP₁₅ formed bythe Condensed Phase method. It is agitated by means of a vibratorgenerally indicated at 314 and picked up by the flow of Argon gasthrough the venturi generally indicated at 316. It then flows into thereactor 304, passing through tube 317 into a steel susceptor 318. Thesusceptor is heated by means of a RF coil 319 to a temperature of atleast 900° C. which causes the KP₁₅ to vaporize. At the end of tube 316,as shown in FIG. 40, a nozzle is formed by incorporating a plurality ofsmall tubes generally indicated at 320 in FIG. 41, having a plurality ofsmall orifices 321. Tubes 317 and 320 are alumina and tubes 320 are heldwithin the end of tube 317 by means of magnesium oxide cement 322.

The KP₁₅ on vaporization dissociates into its constituents and the vaporis carried by the Argon gas through the orifices 321. The film isdeposited on a cooler substrate 324. The substrate may be heated bymeans of hot wires 326 fed by electrical connections 328.

Alumina tube 317 has a one-quarter inch outside diameter and one-eighthinch inside diameter. Tubes 320 have a one-sixteenth inch outsidediameter, are one-quarter inch long and have four one-sixteenth inchdiameter holes that are through.

The apparatus is operated under a vacuum of 0.1 to 0.5 mm Hg. Amorphousfilms of up to 1 micron thick may be formed in runs of up to fifteenminutes. At the end of a run, the substrate 324 reaches a temperature of200°-300° C., depending on whether it starts out at room temperature oris initially preheated to 200° C.

Chemical Vapor Deposition

We have prepared thin films of KP₁₅ by means of Chemical VaporDeposition.

A typical chemical vapor deposition reactor is shown in FIG. 50. It isconstructed of Pyrex. The reactor chamber 401 is a 26 mm I.D.×27.0 cmlong tube in the center of which is positioned a 6.0 mm I.D.×30.0 cmlong tube 402 which serves as both a thermowell and substrate holder.The thermowell is held in position by an adjustable O-ring collar 403.The vent tube 404 allows for the continuous removal of the gaseousexhaust stream. It is attached to a trap (not shown) which removes theunreacted phosphorus before venting of the stream to air. The vent tube404 and O-ring collar 403 are attached to the reactor chamber 401through a 2.0 cm I.D. O ring joint 405. The reactor chamber 401 islocated in a resistance furnace generally indicated at 406.

Molten phosphorus is metered by a piston pump (not shown) through a 1.0mm I.D. capillary tube 407 into a vaporization chamber 408. The moltenphosphorus is evaporated in the vaporization chamber 408 by a stream ofargon which is injected into the vaporization chamber 408 through the6.0 mm I.D. inlet tube 409. The gaseous phosphorus/argon stream entersthe reactor chamber through nozzle 410. The nozzle 410 has an opening of4.0 mm. The evaporation chamber 408 is located in a resistance ovengenerally indicated at 411.

A gascous mixture of potassium and argon is metered into the reactorchamber 401 through inlet tube 412 which has a 6.0 mm I.D. Neat argon,which acts as a shroud for the potassium/argon stream, enters the systemthrough 6.0 mm I.D. tube 413. Both the potassium/argon stream and neatargon stream enter the reaction chamber 401 at 414. The potassium/argonand neat argon lines (412, 413) are located in a resistance ovengenerally indicated at 415.

The substrate 416 is positioned on the thermowell 402. The temperatureof the substrate 416 is determined by a thermocouple 417 positioneddirectly below the substrate 416 on the thermowell 402.

During operation, ovens 406, 411, and 415 are maintained at appropriatetemperatures. The gaseous reactant streams enter the reactor chamber at410 and 414. The exhaust gas mixture leaves the reaction chamber throughthe vent tube 404. The desired film forms on the substrate 416.

The substrates are maintained at a temperature of 310°-350° C., thetemperature being maintained constant to plus or minus 2° C.

In a typical run 1.24 g of white phosphorus and 0.13 g of potassium aredelivered into the reactor over a two hour period. The total Argon flowrate is maintained at 250 ml per minute during the run.

A number of experiments were conducted in which phosphorus/argon andpotassium/argon were fed simultaneously into the reactor. Thephosphorus/argon stream was maintained at approximately 290° C. and thepotassium/argon stream at approximately 410° C. The calculated atomratio of reactants in the reactor was P/K approximately 15. The reactorwas maintained at 300°-310° C. In a typical experiment the liquidphosphorus feed rate was 0.34 ml per hour.

Amorphous KP₁₅ films were prepared using nickel-on-glass substrates. Thefilms are about 0.3 millimeters thick.

With a run time of 1.0 hour, the films produced were found to havenominal KP₁₅ composition. The thickness of the film was dependent on theposition of the particular substrate in the reactor. Examination of thefilms using SEM showed them to be quite uniform.

Purification of Phosphorus

50 grams of Atomergic phosphorus, "99.95% pure", was subjected to a450°-300° C. gradient for 75 days. After this admittedly very long time,21% of the material remained behind and 60% of the charge ended up asamorphous, bulk deposits.

Previous analysis showed the Atomergic phosphorus to be less than 99.90%pure, probably closer to 99.80%, with aluminum, calcium, iron,magnesium, sodium, and silicon as major impurities (all greater than0.01%, and some greater than 0.05%). This material costs about $220 perkilogram. In comparison, "99%" P from Alpha Ventron is $17 /lb., or$37.5 /Kilo.

Table XX summarizes the results of flame emission spectroscopy on threematerials generated by the aforementioned treatment.

                  TABLE XX                                                        ______________________________________                                        IMPURITY LEVELS BY FES*                                                              Atomergic Material   Material                                                                              Material                                  Element                                                                              "99.95"   A          B       C                                         ______________________________________                                        Al     0.03-0.3% 0.02-0.2%  20-200  less than 1                               Ba     3-60      40-400     2-20                                              Ca     30-600    6-60       3-30    less than 2                               Cu     .4-4      20-200     less than 1                                                                           less than 1                               Fe     40-400    0.03-0.3%  4-40    less than 1                               Pb     .6-6      3-30                                                         Mg     0.01-.1%  6-60       3-30    less than 1                               Mn     6-60      3-30       less than 2                                       Mb               .6-6                                                         Ni               3-30                                                         Na     0.4-4%    MC         30-300   less than 20                             Si     0.04-0.4% 0.3-3%     0.02-0.2%                                                                             less than 1                               Sn     6-60      MC         3-30                                              Ti     1-10      1-10                                                         V                0.6-6                                                        ______________________________________                                         *Flame Emission Spectroscopy                                                  All values in ppm, except where noted                                         0.1% = 1000 ppm                                                               MC = major component measured at greater than 1%                         

Material A was a residue, dark brown in color, throughout the chargezone, which did not undergo vapor transport. Material designatedMaterial B was a hard boule of material, light in color, which did notvaporize, primarily because its position in the charge zone results init being at a slightly lower temperature than 450° C. Material C was anamorphous boule in the cold zone.

Clearly, most of the impurities of the charge remain in Material A atfairly concentrated amounts. The high impurity levels would be expectedto give rise to a lower vapor pressure of phosphorus at a giventemperature. The impurity level of the material pretty well reflects thevalues for the initial charge material. The boule, Material C, is apretty pure material, with the sodium content being the major observedcontaminant. Taking the sum of contaminants, at their maximum indicatedlevels, this material has a purity level of 99.997%, at worst. Thecomparable material, obtainable from commercial sources, as 99.999% P,costs about $1,800 /kilogram.

Clearly, we have illustrated a cost effective method for purifying redphosphorus to a high degree

Reinforced Materials

The use of phosphorus compounds as fire retardant additives is wellknown. Because of the highly stable nature of the alkali metalcontaining phosphorus materials disclosed herein, they may be utilizedfor such purposes.

The fibrous and plate-like forms of the materials disclosed herein, forexample, fibrous KP₁₅ and KP_(x) where x is much greater than 15, theplate-like monoclinic phosphorus habit, the twisted tube form ofphosphorus, and the star-shaped material of FIGS. 44 and 45, all showpromise as reinforcing additives for plastics and glass. The twistedtube fibers and star-shaped fibers should be of particular value due totheir ability to mechanically interlock with the matrix of a compositematerial. Their fire retardant qualities should also prove useful insuch materials.

Coatings

As previously discussed, many of the materials disclosed herein formhigh stable amorphous coatings, with good adhesion to metal and glass.The MP₁₅ amorphous films are particularly stable and provide goodadhesion to metal and glass. Thus they may be utilized as corrosioninhibiting coatings on metals and as optical coatings on glass.

A coating of approximately 1000 angstroms on an appropriate infraredoptical component such as germanium, will provide a window transparentto infrared but showing absorption in the visible. Such coatings whencombined with coatings of other materials of differing optical index,can be utilized to provide anti-reflection coatings on infrared optics.

Our experiments show that MP_(x) material can be deposited as films withgood adhesion on steel, aluminum, and molybdenum. The films are ductile,non-porous, polymeric, and non-brittle.

Thus the materials shown herein should find wide application as coatingsand thin films.

INDUSTRIAL APPLICATION

Thus we have disclosed an entirely new class of high phosphorussemiconductor materials. These semiconductors comprise catenatedcovalent atoms where the catenated covalent bonds serve as the primaryconduction paths in the materials. The catenated atoms form parallelcolumns as the predominant local order. Preferably the atoms aretrivalent and have bonding angles that permit tubular, spiral orchannel-like columns. The columns may be joined by atoms of one or moredifferent elements bonded to two or more of the catenated columns.

We have disclosed in particular high phosphorus and mixed pnictidesemiconductor materials of this class. These include high phosphoruspolyphosphides of the formula MP_(x) where x ranges from 7 to 15 andentirely new materials where x is very much greater than 15--for allpractical purposes pure phosphorus.

These materials can be characterized as containing groups of seven ormore atoms organized into pentagonal tubes. They may be characterized ashaving the formula MP_(x) where x is greater than 6 and they may becharacterized as comprised of phosphorus in a molar ratio of phosphorusto any other atomic constituent greater than 6; they may becharacterized as high phosphorus materials where the phosphorus atomsthereof in substantially all local orders comprise phosphorus atomsjoined together by multiple covalent p--p bonds organized into layers ofall parallel pentagonal tubes. They may be characterized aspolyphosphides containing alkali metal atoms wherein the number ofconsecutive covalent phosphorus-to-phosphorus bonds is sufficientlygreater than the number of non-phosphorus-to phosphorus bonds to renderthe material semiconducting. They may be characterized as having askeleton of at least seven covalently bonded phosphorus atoms havingassociated therewith at least one alkali metal atom, conductivelybridging the phosphorus skeleton of one unit with the phosphorusskeleton of another unit; they may be characterized as a polyphosphidehaving the formula MP_(x) where M is an alkali metal and x is at least7.

These materials may be further characterized by having a band gapgreater than 1 eV; from 1.4 to 2.2 eV and for the best materials we havediscovered approximately 1.8 eV. They may be characterized by having aphotoconductivity ratio greater than 5; more particularly, within therange of 100 and 10,000.

These materials may be further characterized by their trivalent dominantatomic species; the homatomic bonds formed by the dominant species; thecovalent nature of these bonds; the materials' coordination number ofslightly less than 3; the materials' polymer nature; their formation inthe presence of an alkali metal or metals mimicking the bonding ofalkali metals with the dominant species; in the cryatalline form, theirpentagonal parallel tubes either all parallel in KP₁₅ -like materials,paired parallel crossed layers in monoclinic phosphorus, or all paralleltwisted tubes in twisted fiber phosphorus; their ability to formamorphous films and boules retaining their electronic qualities; and bytheir methods of manufacture; and other qualities made apparent in thepreceding description.

The amorphous materials we have discovered maintain the electronicqualities of the KP₁₅ all parallel pentagonal tube structure and intheory, at least, it appears that that structure is maintained in thelocal scale in our amorphous materials. However, we do not wish to bebound by any particular theory in this matter. In particular, the claimsappearing below should be interpreted broadly to cover all aspects ofour invention, regardless of later acquired knowledge that might be saidto conflict with the theories and hypothesis we have put forth, bothexplicitly and implicitly.

We have disclosed junction devices, photoconductive (resistive) devices,photovoltaic devices and phosphors made from these materials.

We have disclosed resistance lowering dopants, namely Nickel, Chromiumand Iron, leading to the conclusion that substantially the entire groupof atomic species having occupied d or f outer electronic levels may beutilized if of the appropriate atomic size.

We have disclosed resistance lowering substitutional doping with Arsenicwhich indicates that all Group 5a metals may be utilized.

We have disclosed junction devices having a back contact of Ni, Nidiffused therefrom, and top contacts of Cu, Al, Mg, Ni, Au, Ag, and Ti.

We have disclosed new forms of phosphorus wherein the local orders areall substantially parallel pentagonal tubes, twisted fiber phosphorusand monoclinic phosphorus. We have formed these new forms of phosphorusby vapor deposition. The all parallel and monoclinic form require thepresence of an alkali metal during deposition.

We have disclosed both amorphous and polycrystalline films of MP₁₅ whereM is an alkali metal. We have constructed various semiconductor devicesfrom all of the all parallel pentagonal tube materials, including wafersof MP_(x) where x is much greater than 15, including a new form ofphosphorus, amorphous thin films of KP₁₅ and amorphous thin films ofKP_(x).

We have disclosed methods of making metal polyphosphides and two newforms of phosphorus by controlled two temperature single sourcetechniques.

We have disclosed methods of making our high phosphorus materials by twosource vapor transport.

We have disclosed a method of making high purity phosphorus.

We have disclosed methods of making crystalline and amorphous forms ofMP_(x) where x ranges from 7 to 15 by condensed phase methods.

We have disclosed chemical vapor deposition, flash evaporation andmolecular flow deposition methods.

Industrial applications of the semiconductor materials and devices wehave discovered are mainfest, they run the whole gamut of semiconductorapplications. The crystalline materials may be used as reinforcingfibers and flakes for plastics, glasses and other materials. Thematerials of our invention may be used as coatings on metals, glass, andother materials. The coatings may protect a substrate from fire,oxidation, or chemical attack. The coatings may be employed for theirinfrared transmitting, visable light absorbing qualities. They may beemployed with other materials as antireflection coatings on infraredoptics. The materials may be used as fire retardant fillers andcoatings. Monoclinic phosphorus may be used an an optical rotator.

It will thus be seen that the objects set forth above among those madeapparent from the preceding description are efficiently attained andthat certain changes may be made in carrying out the above methods,processes and in the above articles, apparatus and products withoutdeparting from the scope of the invention. It is intended that allmatter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

It should be understood that we have used crystalline to mean singlecrystals or polycrystalline material unless otherwise stated. Amorphousas distinct from single crystal or polycrystalline, means amorphous toX-ray diffraction. All periodic table references are to the tableprinted on the inside front cover of the 60th edition of the Handbook ofChemistry and Physics published by the CRC Press Inc., Boca Raton, Fla.Alkali metals are identified thereon and herein in Group la andpnictides in Group 5a. All ranges stated herein are inclusive of theirlimits.

By semiconductor device we mean any device or apparatus utilizing asemiconductor material. In particular, semiconductor device includesXerographic surfaces and phosphors regardless of how they are excited,as well as photoconductors, photovoltaics, junctions, transistors,integrated circuits and the like.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention anddiscovery herein described and all statements of the scope thereof whichas a matter of language might be said to fall therebetween.

Particularly it is to be understood that in said claims, ingredients orcompounds recited in the singular are intended to include compatiblemixtures of such ingredients whenever the sense permits.

Having described our inventions and discoveries what we claim as new anddesire to secure by Letters Patent is:
 1. A phosphorus material formedas the deposition product of vapor transport from separated heatedsources of phosphorus vapor and the vapor of one or more metals, each ofsaid sources held at a high temperature, said product being deposited ina deposition zone located between said sources, said deposition zonebeing held at a substantially lower temperature than said sources, andthe atomic ratio of phosphrous to metal in said product being greaterthan
 15. 2. A polycrystalline high phosphorus material formed as definedin claim
 1. 3. An amorphous high phosphrous material formed as definedin claim
 1. 4. A high phosphorus polyphosphide formed as defined inclaim 1, having the formula MP_(x), wherein M is one or more metals andx is equal to or greater than
 15. 5. A high phosphorus polyphosphideformed as defined in claim 4 further comprising at least one otherpnictide.
 6. A high phosphorus polyphosphide as defined in claim 4wherein M is one or more alkali metals.
 7. A high phosphoruspolyphosphide as defined in claims 4, 5, or 6, wherein x is greater than15.
 8. A solid stable material having the formula MP_(x) where M is oneor more alkali metals and P is one or more pnictides, primarilyphosphorus, and x is greater than
 15. 9. The material defined in claim 8wherein said material contains less than 100 parts per million of M. 10.The material defined in claim 8 wherein said material is in the form ofa wafer.
 11. The material defined in claim 8 wherein said material is inthe form of a film.
 12. The material defined in claim 8 wherein saidmaterial is in the form of a thin film.
 13. Amorphous material asdefined in claims 8, 9, 10, 11, or
 12. 14. Polycrystalline material asdefined in claim 8, 9, 10, 11, or
 12. 15. The method of preparingpolyphosphides of the formula MP_(x) where M is one or more metals and Pis one or more pnictides, primarily phosphorus, by vapor transportcomprising providing two heated separated sources of phosphorus and oneor more metals and a separate deposition zone having a substantiallyconstant temperature over an extended area, said temperature beingsubstantially less than the temperature of said sources and the atomicratio of phosphorus to metal in said polyphosphides being greater than15.
 16. The method defined in claim 1 and the additional step ofdiscontinuing providing vapor from said metal source and continuing toprovide phosphorus from said phosphorus source for deposition in saidconstant temperature area.
 17. Metal polyphophides of the formula MP_(x)where M is one or more metals and P is one or more pnictides, primarilyphophorus, said metal polyphosphides being prepared by the method ofvapor transport comprising the steps of providing two heated separatedsources of phosphorus and one or more metals and a separate depositionzone having a substantially constant temperature over an extended area,said temperature being substantially less than the temperature of saidsources and the atomic ratio of phosphorus to metal in saidpolyphosphides being greater than
 15. 18. A new form of substantiallypure phosphorus of the formula MP_(x) where M is one or more metals andP is one or more pnictides, primarily phosphorus, said new form ofsubstantially pure phosphorus being prepared by the method of vaportransport comprising the steps of providing two heated separated sourcesof phosphorus and one or more metals and a separate deposition zonehaving a substantially constant temperature over an extended area, saidtemperature being substantially less than the temperature of saidsources and the atomic ratio of phosphorus to metal in saidpolyphosphides being greater than
 15. 19. Polycrystalline product asdefined in claims 17 or
 18. 20. A thin film of product as defined inclaim
 19. 21. Amorphous product as defined in claims 17 or
 18. 22. Athin film product as defined in claim
 21. 23. A crystallinepolyphosphide wherein the crystals are in the form of star shaped rods.24. A crystalline polyphosphide wherein the crystals are in the form ofstar shaped rods condensed from the vapor phase at a temperature below500° C.
 25. The polyphosphide defined in claim 24 condensed atsubstantially 462° C.
 26. The metal polyphosphides of claim 17 whereinsaid method of vapor transport for preparing said metal polyphosphidesincludes the step of discontinuing providing vapor from said metalsource and continuing to provide phosphorus from said phosphorus sourcefor deposition in said constant temperature area.
 27. The new form ofsubstantially pure phosphorus as claimed in claim 18 wherein said methodof vapor transport for preparing said new form of substantially purephosphorus includes the step of discontinuing providing vapor from saidmetal source and continuing to provide phosphorus from said phosphorussource for deposition in said constant temperature area.